2 Crossfired HD 6970 vs 1 HD 6990, which is best?

[dreamer2008]

I looked today for a HD 6990 to buy and couldn't find one. But I could find HD 6970. So, in theory, 2 6970 cards in crossfire should perform the same as 1 HD 6990, right?

[Oldminer]

1 x 6990 will give you a higher hash rate..marginally..

https://en.bitcoin.it/wiki/Mining_hardware_comparison

Oh and dont CF them

[dreamer2008]

1 x 6990 will give you a higher hash rate..marginally..

https://en.bitcoin.it/wiki/Mining_hardware_comparison

Oh and dont CF them

Thanks for the reply. I know that page, I look at it constantly when deciding what to buy.

I know that one 6990 would be best, but I can't find any store in my country that sells it, they are all out of stock. And I wouldn't like to buy it from amazon and wait for it 1 or 2 months. In a few days I would like to start mining.

And why shouldn't I CF them?

[Oldminer]

1 x 6990 will give you a higher hash rate..marginally..

https://en.bitcoin.it/wiki/Mining_hardware_comparison

Oh and dont CF them

Thanks for the reply. I know that page, I look at it constantly when deciding what to buy.

I know that one 6990 would be best, but I can't find any store in my country that sells it, they are all out of stock. And I wouldn't like to buy it from amazon and wait for it 1 or 2 months. In a few days I would like to start mining.

And why shouldn't I CF them?

Personally I'd just go with the 2 x 6970's rather than wait.

And with regards CF, most people report lower hash rates and I experienced the same when I CF'd my 2 x 6950's

[dreamer2008]

Personally I'd just go with the 2 x 6970's rather than wait.

And with regards CF, most people report lower hash rates and I experienced the same when I CF'd my 2 x 6950's

Thanks you, that's what I thought.

I have never CF two cards, is it something that I can change easily in the settings, or is it more complicated?

[xurious]

If you have the slots, then pick up a pair of 6970's. This way if one card dies you can still be using the other.

If you lack slots and have extra cash, then the 6990 is a good way to.

[cicada]

Possibly marginally better power consumption from the 6990.

Figures I've seen put the 6970's at ~180-200W at full-bore (400W total), vs ~375W for a 6990.

I don't own either so this is pure speculation based on other reports.  It would make sense for the 6990 (basically two 6970's) to be a little better power-wise since they share a PCB (less overhead)

[dinzy]

I wouldn't doubt better power performance on the 6990 because it eliminates some redundancy which is electrically lossy. 

There are 2 things to consider.  How long you intend to mine, and do you intend to keep the card(s) or sell them.

It is not clear if the 6990 will hold it's value the same or better than the 6970x2 over the long haul, but given it's scarcity now you could probably unload it near cost.

[kcobra]

Seems like to me dual 6970 cards should give a higher hash rate than one 6990. A 6870's default clock is 880 mhz while a 6990's default clock is 830 mhz. Also, you would think a 6970 could overclock higher than a 6990 as heat would not be as much of an issue.

For my money I would go with dual 6970. Of course unless you are simply wanting to supplement the cost of a 6970 crossfire gaming rig with some mining I would not spend $600+ in order to get ~800 mh/s mining capability.

[dreamer2008]

Thank you for the replies!

Since I couldn't find any store in my country that has at least one HD 6990, I focused on the other options. And I switched to the HD 6950 option instead of 6970, since it is cheaper and with a good mining performance on paper.

[Oldminer]

Thank you for the replies!

Since I couldn't find any store in my country that has at least one HD 6990, I focused on the other options. And I switched to the HD 6950 option instead of 6970, since it is cheaper and with a good mining performance on paper.

You will be happy with the 6950's - their a solid card. Just check the PSU requirements.

[cicada]

+1 on the 6950's, I've got 4 of them running right now, stable for a couple of weeks, ~345mhash/s each without too much tweaking.

If you're really lucky, you'll get a card with unlockable shaders, and you've basically just gotten a 6970 at a discount.

[airdata]

6970s are in stock.  From looking at comparisons I'd assume 2 6970s would do the same as one 6990. However a big 6990 perk is density.

[Jack of Diamonds]

You can pull 410-430mhash per core on a 6990 (up to 860mhash/s per card) and it takes only 1 PCI-e slot.

It also consumes less power than two 6970's so it's essentially the best single mining card if you can pick it up for around $700 bucks.

Sure you can get nearly the same hash rate with two 6970's but that will take up half of your motherboard.
If you have 4 slots, you can use 4 6990's for 8 GPU's.

Whereas you can only fit 4 6950 = 4 gpu's on a typical motherboard.