I have a ATI 5870 2GB which works very well for me which I was planning to Xfire at some point in time. Newegg recently came out with a ATI 5970 2GB at a price to hard to resit which I got. I thought this a nice solution since the 5970 is essentially 2 underclocked 5870's on a single card which makes it seem like these should xfire very well together once clocked similarly. The questions I have are, if not clocked similarly will these still work well together at different clocks. Also is the 2gb 5970 gonna handicap the set up as it's creating 2 1gb 5870's and with a 2gb 5870. Or will it work like 2 2gb cards?
the vRAM on the 5970 is shared between the two gpus, they don't each have 1GB. So your setup will have 2GB total vram since all ram is simply mirrored.
You won't have to change clock speeds but it's possible you will get micro-stuttering if you don't. Micro stuttering is when one frame is displayed faster than the others causing things to look less smooth.
What resolution are you playing at? Likely micro stuttering won't be a problem since 3 gpus usually fixes it. If it is, and if you notice it (many people don't), you'll likely be able to remedy it by downclocking the 5870.
What motherboard are you using? If the PCI slots are too close together, that is going to be a hot setup.
Not sure if that's the exact model, i don't believe so, but the layout is very similar.
Also something I've been wondering, I think if If Xfired ,the PCI-E first slot is 16x and the second goes to 8x. I should put the 5970 as first card and the 5870 as second correct? I believe it will get very hot in the case but i'll monitor the temps when it comes. I was thinking about trying to add an after market cooler so I could possibly get the 5970 clocks to the default 5870's.
Edit: Playing at 1920-1200. Hoping to eyefinity soon with 3 1920-1080's though
Will my 750W power supply be sufficient for this setup?
I'll install it to the bottom as soon as it comes. Will the 8x matter that much instead of the 16x for the 5970? Would it be wise to upgrade my motherboard to a 990FX (though I heard 1090FX will come out this year). Or is it not worth it from a performance/price perspective to go from a 790x to a 990fx?
For x8/x16, the difference would be minimal for the 5970 but there would be a difference. For the 6990 (6xxx's dual gpu card) it's about 10-15% and It'd be a bit less for the 5970. I'd look it up though. Doubt it's worth upgrading.