7790 vs 7870

[Veldrik]

Hi all,
Firstly, I'm new, hence posting a hardware question in the newbie forum. - Hello!

So I'm looking for advice on what card to add to my "rig".

I'm running a (Gigabyte OC) 7870 on an Intel i3 2500k with a bunch of 1tb and 512 barracudas and samsung platter drives.
Currently I'm pulling 404mhash/s with the full system running at 212kWh under windows server 2008r2 running cgminer.  The system idles at 110kWh.  The card runs at 57*celcius, with about 70% fan load just after midday.

I want to add a second card, and since I am in Australia, the power here is 0.27c/kWh, and hardware isn't cheap (hence not building a dedicated rig yet).

So the best options I can find for initial cost (#/$) and long term cost (#/kWh) comes down to:
another 7870 at $199 (this time a sapphire n/OC straight up GHZ version, probably version 1 bios - Dual X fans - the last one in stock, all other 7870s over here start at $225 and jump to $250 for XT or OC versions)
or a 7790 OC at $158 (sapphire dual fans)
or a 7790 n/OC at $149 (sapphire - single fan)

I have a Gigabyte 7870 at the moment, but I assume the sapphire can be overclocked up to the same 400mhash/s, or atleast 390 and isn't much different in energy efficiency

So I'm mainly after information about:
a) performance of the 7790:  mhash/s and power consumption.   I have seen some reporting of 300mhs at 80watts, and and the rest of then running at 245mhash/s stock, or 275 when OCed.  Not really enough of a sample size though so any more information would be fantastic
b) if there are still driver issues when running a 7790 side by side with any other 7xxx cards - in particular a 7870.  Apaprently at release since they had a "performance" driver they conflicted when operating under OpenCL.  According to the release notes for both the latest catylist driver and for the beta driver, the drivers have added support for 7790.  If anybody knows if this has been fixed that would be great.

At the moment I mine BTC.  I might goto LTC soon, which I think would favour the 7870 due to the memory size (2gb vs 1gb).  Although I'm not sure by how much, due to the difference of mhash/s vs power.

Cheers!

Other info - I found that 7950 and 7970s were out performed by the 7870 due to power consumption, that and they cost more than twice that of a 7870 over here (in Australia) so it's initial cost #/$ is significantly lower than pretty much anything except a 7750.
7770s are around $89.

[Sofi]

7870 are around $280

[Veldrik]

Then I guess I'm blessed that in Sydney 7870's aren't that expensive.

[liquidkore]

I'm running an HIS 7870 GHz edition at 420MH/s that I picked up on craigslist for $180.00.

Miner Settings:
GUIMiner 2012-11-18
-v -w 128
CPU 0 (i uncheck 1,2, and 3 because I'm also mining litecoin on the same box @30KH/s)

GPU Settings:
clock: 1155 Mhz
mem clock: 350Mhz
fan: auto
voltage: auto
temp = 65c

[razoredge]

whatever you do, realize that in 6  to 12 months we may all be using ASICs

[Veldrik]

I sure do, and currently the first 7870 will pay itself off in around 70 days unless btc bottoms out to rapidly (say 0.4USD by the end of May).
And since I game on NVidia cards and only have the ATI card solely for BTC/LTC, if I flog it off for atleast $100, I'll still be ahead.
And there is always LTC.

[Veldrik]

oh, and if it does pay itself off and ASICs don't start flooding until August, I'll be flogging off the cards (although if I get an 7790 i might keep it as it apparently supports sli) and buying an ASIC myself.  Lower power is always a good thing.

[liquidkore]

You might want to also take a look at going this route:
https://bitcointalk.org/index.php?topic=179769.0

I have an order in for 60 chips (3 boards of 20 chips/ea), which is roughly ~17GH/s @ 20watts, or ~฿5.90/week

[Veldrik]

You might want to also take a look at going this route:
https://bitcointalk.org/index.php?topic=179769.0

I have an order in for 60 chips (3 boards of 20 chips/ea), which is roughly ~17GH/s @ 20watts, or ~฿5.90/week

That's nice - he also offers double density boards.

I quite like the layout he has too - simple and expandable - I'll have to look into that. - Cheers for the info Liquidkore