2 8800GT's but there isn't a need for it to be honest.. and also the 98xx series looks to be mainly 2 8800 gts g92 slapped on one board for twice the cost of 1.
but in the respect of gt vs gts go with the 512 gts and it will out perform the gt, but not by a huge amount.
also the q6600 can oc to 3 easily and most people can keep it stable around 3.2~3.4 so don't wait/waste your money on something that will be around the same performace as a q6600.