Which brand of card is this? what clock settings are you using?
it's allright
i got 8 7950 radeon vapor x on 2 MB.
I use the overclock button and get 550 now (switch over 64bit and add loads of ram 16/MB).
I'm sure by tweaking a bit i can get more but for now i'm happy.
I'm pretty sure that my windows 7 was 32bit before and recognized 7.2 or something gig of ram but this was not enough for 4x7950