I have a question that torns me apart for some time now, so may be with few opinions I can finally make up my mind
I'm setting up crossfire for my rig, which is supposed to run heavy calculations via OpenCL (neural networks, for those interested), so I'm looking for max GFlops I can get (yes, I know that OpenCL doesn't need a crossfire, I just use this term just as a shortcut). With my budget for now I can afford either 4x7950 cards, or 3x7970. Of course, 3x7970 would be preferable, cause this leaves upgrade possibility for future by adding one more card. I started to look at what's available now, and all cards have some problems:
1. Sapphire 7970 Vapor-X GHz edition. Looks good, but takes 2.5x slots, so there is no way to add 4th card in a future.
2. Gigabyte 7970 Windforce GHz edition. I like the performance (tried Gigabyte 7950 Winforce before - cool and quiet), and the fact that it's clocked 1100Mhz right ouf of the box, but have 2 problems: first, one review on Newegg says that initial voltage is already over 1.2V to achive that speed; second, lots of people comment on VRM temps reaching 105-115 degrees C on this particular card due to bad VRM heatsink design.
3. XFX 7970 GHz edition. Can't find any "official" review, but all non-Ghz edition reviews for this card claim that it is hot and loud, so having 3 of them side-by-side will probably be no-go. And I don't like to have a too much noise.
4. HIS X 7970 GHz edition - too expensive, plus I had bad experience with previous HIS card - the overclock is non-existent on them, plus cooling is barely efficient.
5. VisionTek 900557. No reviews anywhere, but price is very tempting. Memory clock for this one look suspiciously low (1425 vs 1500 on all other GHz editions). Still, might be this one is the way to go?
Non-GHz editions are cheaper, but they are really shot in the dark, as they might, or might not overclock, and shipping badly overclocking cards back and forth to Newegg will eat this price difference pretty fast.
PCS+ 7970 has 1100 MHz right out of the box, but no heatsinks on VRM and memory at all, plus it is 2.5 slot card.
On the other hand, 4x7950 cards will cost me less than 3x7970, and will give me about the same number of TFlops, but will take away possibiliy to add more. On a plus side - my temps will be lower. On a negative side - 7950 is a "broken" 7970, i.e. chips where some transistors can't pass QC or are outright broken, so AMD just lowers number of processing units and blesses this former 7970 chip as 7950. Problem is that bad silicon is bad silicon - it has more chances to die down the road than those 7970 chips that passed QC with no problem.
Also, please don't recommend MSI 7950 TwinFrozr - I had 2 of those in a crossfire setup, and they were loud as a rocket, with temps reaching 91 C - no way, thank you. Had a very nice experience with Gigabyte 7950 Windforce, but didn't check the VRM temp, so not sure about them.
Probably I can get away from most of these problems by using watercooling, but this is something I'm not ready for yet - heatsinks are over $100 each, plus a hassle with extra radiator(s) and pump, and overall inconvinuence
If only they had 7970 with NO issues!
So, any thoughts or comments? I'm agonizing over the decision more than for month now
In case anybody reading this: I finally made up my mind after some more reading. I'm going with Gigabyte 7970 Windforce GHz edition. It turned out that 115C temps for VRM is OK, because they are designed for 125C, so the only minus left is initial voltage that is over 1.2V, but I decided to ignore that, and try anyway how it'll work for me.