You need a Mini (or one of the Gigabyte ITX or MSI similar-size cards) at the end slot, as there is ZERO SPACE between the middle card and the end card, so the only airflow into the middle card is going into the part of the end fan that the Mini leaves unblocked.
This was my standard configuration for my "Folding" rigs as risers KILL throughput on Folding (there is a LOT of work done on the CPU and a LOT of bandwidth needed for data transfer, even a PCI 2.0 8x slot shows measurable impact on Folding PPD on high end cards).
If you used hybrid cards, PROBABLY you could get away with 3 full-length cards as most of the cooling is via the radiator - that would definitely work on one of the "full card waterblock cooling" type cards like the MSI Seahawk.
If you are going to go the watercooled route though, you might want to go with one of the "4 full-length PCI-E slots" motherboards like the Biostar Racing Z170GT7 or the alternatives from ASROCK, ASUS and the like - if you can find one at a reasonable price.

Phil has posed about a build with one of the Onda boards (the one with the wider spacing I think?) that will end up with 4 1080 ti and 4 1070 ti cards on it.

HD 7870 can mine ZEN/ZTC/ZEC, I think they are good for somewhat around 150 sol/s but it's been months since I had mine doing that so I might misremembering somewhat.

 Your CPU is a tolerable but not great Monero (or any other Cryptonight coin) miner.

 Ignore any coin on an algorithm that has ASIC hardware available - specifically including Bitcoin (SHA256), Litecoin (Scrypt), DASH (X11), and such.

 Should be quite close to the 780 ti, if you can find anyone that posted specs on THAT OLD of hardware.

 I doubt it's going to be a good ETH miner, but should do fairly well on ZEC - I'd *GUESS* 1070 to 1080 level hashrate.

I generally prefer, on multi-PS setups, to power the riser and the GPU power connections from the same power supply.
I'm PRETTY SURE that the cards themselves don't "merge" the inputs though, so it should be safe to power them from different supplies - just more likely for the card to get "confused" if one power supply starts up faster than the other and not be sure if it HAS proper power.

Cryptocoin mining is low bandwidth, so the use of even 1x slots works fine with little or ZERO impact on hashrates.

 There are other stuff you can do with a PC that IS bandwidth-intensive though, like Gaming or running the Folding@home client, where anything less than a 8x PCI-E 3.0 or 16x PCI-E 2.0 slot can have a measurable impact.

Don't bother mining DOGE directly - it's mostly mined through "merge mining" from folks using ASIC miners to mine Litecoin the last 2-3 years, since shortly after it moved to being "merge mineable".

And it's DOGE not DODGE.

Should work fine, just configure the miner to not use the card you're gaming on.

 Nicehash pays out in BTC but it pays you for hashrate on many different algorithms.

Unless it's a single-slot GPU, it's also going to block 3 of the 1x slots (and possibly 6 of them if it's a WIDE card like an Aorus or Amp Extreme).

 It DOES work, that's how I've got mine set up right now - but I'm only running 6 total cards on the thing right now, 5 on risers between banks A and B and one in the 16-bit slot.

Gigabyte and Inno3d (and possible a couple other folks) have ANNOUNCED cards, but I've not seen them available for sale anywhere YET.

 Based on the published specs, they are likely to be POOR ETH performers (worse than a standard 1070 due to their use of GDDR5X instead of GDDR5) and probably about the same on anything else.

 Given the 4GB that's been announced on most of them, they SHOULD price less than the 1070 - but how much less is a good question.

 I would also be VERY wary of anything out of Gigabyte, they tend to put JUNK sleeve bearing fans on anything but their Aorus line.

ETH, no.

 Quite a few other altcoins, yes.

 Try running the Nicehash Legacy miner on it to look for good options on what algorithms to use, which will lead you to what coins to mine with it.

At 59C, card lifetime should exceed the warrentee and be measured in years.

 75% fan, if you have cards with good BALL BEARING fans, should also have a lifetime measured in years - but might want to turn them down some, 50-60% should keep the cards under 65C which is a better "balance" on card vs fan lifespan.

 If they are NOT ball bearing fan cards, expect to replace the fans WELL before warrentee period runs out - even if you turn them down, which WILL help some.

2 12 card rigs will tend to be a LITTLE less expensive than 4 6-card rigs - but if one rig goes down that's a LOT more lost income, and it's more of a pain to troubleshoot.

 They're also a bigger pain to set up in the first place, though if you can find a B250 Mining Expert MB at a reasonable price it reduces the pain somewhat due to the on-board multi-PS management.


 In my case, most of my rigs are 5-card because I already have the MB/CPU/RAM/HD from "left-over" FAH rigs and because I can configure them EASILY to run on about 6 amps of power per rig (which lets me put 2 rigs on a standard 15 amp US 117VAC circuit SAFELY).
 They're not the most OPTIMAL rigs possible, but I make up some of the difference by having the CPU mining Monero (or working Gridcoin for some I've not "converted" to full up riser-based mining rigs yet).
 

 It can, if you set it to point at that wallet.

 No availability on the X-850 or SS-860 any more, since Seasonic moved to junk Focus and Prime models (WHY OH WHY DID THEY MOVE TO A JUNK FANCY-NAME SLEEVE BEARING FAN IN THOSE??).

 If I could still FIND X-850 (or even the SS-860) at anything less then RIPOFF pricing when available at all, I'd be sticking with them.


 As far as Nicehash suspending payments on low-balance Bitcoin for now - have you looked at TRANSACTION FEES THIS MONTH?
 There would be cases where the TRANSACTION FEE would *LITERALLY* be equal to 14% of the balance being transfered right now.

 That is based on a transaction I made today that cost me .00145 for the FEE via Electrum on a "within 25 blocks" setting - anything lower was getting "low fee" warning that usually amounts to "it might go through in a week, it might take a month".
 That is also a bit of a DROP from shortly before Christmas, when it was taking almost DOUBLE that fee to get a transaction to not get the "low fee" warning and even WITH that crazy-high of a fee NewEgg/BitPay STILL had issues with the payment.

 If they're still "holding" the smaller transactions next week, iffy.
 If they're still "holding" them by mid-January, THEN it's time to start thinking "scam".

 Apparently not right now - and given how crazy-high transaction fees are right now, it actually makes some SENSE to hold off on the "once per week" balance payments - the transaction fee in some cases would bloody near EQUAL the transaction amount itself.

 This is USUAL for this time of year, transaction fees should start dropping anytime now and probably take 2 weeks to a month to get back down to "normal".

 This is also why I try to avoid buying stuff in December and early January with Bitcoin, the demand and number of transactions skyrockets causing high costs and LOTS of issues.

It is debateable if this one, EBWF, or BMiner is "the fastest" - seems to depend a lot on specific cards and settings ON each card.
This one SEEMS to do better on the "lower end" Nvidia cards like the 1060 and 1070, EBWF seems to do better on the 1080 ti, the middle is a muddle.

If Bitcoin collapses under $10k very soon and STAYS there for a month or more, I'd bet against the Avalon 821 being priced under $2500 at "retail pricing" when it is released.
Given the current recovery from what appears to have been a market correction, I would bet that it is unlikely to be under $3000.

 Up side - unlike the Innosilicon A4+, the distributors seem to be willing to sell singles, and NO worries about customs hassles if you're in the same country as one of them (or in the EU if there's a European distributor somewhere).

 Efficiency affects NET earnings quite a bit, unless you have free power available in a capacity greater than you can afford to buy miners to fill up.

 Nope, the interface is completely different IF it exists at all under AMDGPU-PRO - that's a question I've been trying to find an answer to for many months (and most recently did ANOTHER round of web searching yesterday) and have yet to find an answer.

 AMD is WAY overdue to release a replacement for aticonfig from the fglrx days, though I'd REALLY prefer for MSI to release a LINUX version of Afterburner.

Chrome can disable hardware acceleration.