overall I think the GTX 590 is a real mixed bag.

-The minimum Frame rates are really good
-The temps are mind blowingly good (no one could have called this...)
-The power consumption is ok
-The physical size is impressive
-The noise output is really good....

But the overall perf is lower then a 6990 on average. I would say an average of about 5-10%. The thing that makes that really hard is that in some games it performs really really well in others not at all. Also it the high res high settings performance is all over the map as well. the 6990 beats it in Just Cause 2 at 2560 pretty decently but then the GTX 590 under surround.... but close to the opposite is true in AvP. Performance seems to be game Dependant.... the big thing for me tho is how little these seem to OC on stock voltage... they really dumped the voltage off to get the power under the 6990 and it seems to hurt the OC of the card a bunch. however I would like to see some OC results with some extra core voltage in afterburner.... that could make it far more attractive considering that you could get away with it on the stock cooling without getting crazy loud or hot....

it comes down to price I think which puts it neck and neck with the 6990....

I would say it is a more "N00B friendly" card considering that it's smaller and cooler and whatnot so for non enthusiast I would say its the better buy. for most XS users tho the 6990 seems to be your better bet considering the better performance. however added voltage in OCing could change all that.