T-Break published a comparison review between the ATI 2900XT (Xfire) and NVIDIA 8800 Ultra video cards A quote from the article:

If you had $800 to spend on your graphics card, would you be better off getting the 8800 Ultra or a pair of Radeon HD 2900XTs running in CrossFire mode? That is exactly what we find out today.

>> ATI 2900XT (Xfire) vs. NVIDIA 8800 Ultra Comparison Review