According to wiki FX3700 uses same chip with 8800 GT/GTS. There is some benchmarks, but that fact your friend is probably going to use SLI (2 x FX3700 you said, right?) make it a little difficult to compare. SLI goesn't give double performance, it give you around 1.5x more performance than one GPU.
For Linux gaming, since there is no OpenGL4-only games yet, I think it's enough. Windows gaming is different story - now game developers make DirectX11-only games that just doesn't work on DX9/10 generation hardware, like FX3700.
Originally Posted by Nikolai_D