No.
Guessing you may want to go CrossFire, you may want some infos on Nvidia and ATI at the moment.
The new 8800GTS 640Mb from Nvidia blows two 7950GTX Nvidias running SLI in smaller resolutions gaming.
The new 8800 from Nvidia blows anything on the market right now, crossfire/SLI or not (unless you're going for high resolutions, CF/SLI is winning, but you need the latest cards for that...)
You may want to wait for ATI's answer to the 8800 if you want something powerful. I don't know if you plan to stick with ATI or going Nvidia, but if you plan on going dual-cards you'd better check which cards you may want. Dual X1900 running in Crossfire will be beaten by a single 8800GTS 640Mb.