Echo - if this works sorry for the delay but I've been suffering the exact same problem with my kit, and I bought new mobo/cpu/ram/psu as well so tracking the problem was fun. My test was in Ghost Recon : AW, even the intro movies would start at some obscene fps then rapidly drop to 3/5 fps. In game it would trickle up to about 60 then rapidly drop to 12-21fps.
To put this in to context I was on the phone to BFG (USA) for over an hour and they said to RMA it (reminder to self tell ocuk tomorrow). The problems (for me) were firstly nub-error, secondly bios settings.
Firstly, I was able to take the memory ratio to it's slowest 1:1, leaving everything else at default. This made everthing work, so firstly give that a try to see if the gfx card or not - the fps wont be benchmark level but it wont drop.
The shaming noob mistake I made was thinking the motherboard was like my previous 10, with my two 1Gig sticks sitting side by side in slots 1 and 2. To get dual channel, they needed to be in 1 and 3, leaving 2 and 4 empty - hell its even colour coded, but once in the case it was hard to see dark-blue from black and covered in cables.
Once my user-error had been corrected, it was time to get the memory up to its potential. The motherboard (abit aw9d) did not auto detect the setting correctly at all, so I changed the voltage, ratio, and the timings according to the Corsair site.
Back into ghost recon, tested it out and im now getting the blistering performance I dreamed of, and was extremely happy from being close to tears the week previous from getting nowhere.
Really hope this works out for you too.
Bolly
edit: running 97.02 on a 8800GTX, Duo E6600, Abit AW9D mobo, 1Gb Corsair 6400C4x2 - nothing overclocked (sorry)