Im guessing one 6990 is more than enough to handle any game at max settings like max payne, aliens.etc with ease?
Ive tried using both cards and performance seems to degrade actually
Four GPUs have higher overhead; therefore the performance degrades. Only at huge eyefinity resolutions where one 6990 is not enough you may see an improvement. If you had 3 monitors, then you might have benefited from 2 6990s.
No......In Guru3D's test suite one 6990 gets you 762 fps .... the 2nd 6990 gives you a measly 18% improvement to 903.....and that's a $1500 investment. Ya can get 862 fps outta the box with two 900 MHz 560 Ti's for $410 ..... or 95 % of the performance of two 6990's for 27% of the price.
I know driver support for 4 gpu's isnt the best and many games don't even use them.
AMD seems to have licked the 2-way CF issues but tri and quad fire is a place I wouldn't go
The one recommendation we always gave you guys is to keep it simple at 2 GPUs maximum, as after 2 GPUs in a CrossfireX setup you quickly run into weird anomalies that can be irritating. ..... AMD still isn't up-to snuff at the level of NVIDIA though, multi-GPU supports still literally and directly remains the Achilles heel of ATI's Catalyst drivers.
So let's round things up, personally we always say stick to one or maybe two high-end cards as there is so much less driver fuzz to worry about. It's like this with ATI, once you pass 2 GPUs you'll often find yourself compromising a lot with new game titles versus multi-GPU support. And this is why today's tested products in 2-way CrossfireX mode work so well.
AMD really does needs to step it up a little more on better and even faster game profile support AND user based and created profiles, period.
Crossfire then? Heck how do we justify that? Well... it's cool, funny and lovely to play around with but there's no way we can rationalize 1200 EUR for four GPUs to play some games on. Now one card with two GPUs, if properly supported scales extraordinary well. With 4 GPUs setup in CrossfireX mode, well... things get increasingly difficult. In some games the performance of four GPUs is magnificent, in others 4-way multi GPU mode does not kick in, and then in other scaling becomes an issue whether or not that is driver or CPU limitation related. ..... So CrossfireX is absolutely lovely as gimmick and to fool around with. It's however not a questionable enough solution as the negatives very likely do not outweigh to positive.
And not to just puck on the red team, the 590 is just as much of a dog in SLI as the 6990 is in CF