The SLI configuration with two GeForce 7900 GTX cards is an obvious leader in Doom 3 since this game’s conditions (OpenGL plus stencil shadows) are favorable for the GeForce 7 architecture. The GeForce 7950 GX2 is somewhat slower, but it doesn’t matter much as it gives you a frame rate of over 80fps anyway. The Radeon X1900 XTX is competitive in Doom 3 , yet is hopelessly behind the new flagship from Nvidia.
You may find playing this game on a GeForce 7950 GX2 not very comfortable in 16xs mode or in 1600x1200 with enabled 8x FSAA. Note, however, that the Radeon X1900 XTX doesn’t support FSAA higher than 6x, and two such cards are hardly faster than a single 7950 GX2.