Cycle got problem with GPU render

I have just bought Quadro FX 4800 and trying to use it in Blender.
The 1st problem : I found that GPU render ( both support and experimental GPU rendering ) is slower than CPU render ( i use Athlon II x4 930 ) . It was a bit shock cuz i though it can never happen.
2nd problem : wenn i turn on GPU render, Blender crash everytime i switch into Live rendering view .
Can some one explain those problems for me ? i don’t want to waste my money on this Fx 4800

I hope you didn’t get the Quadro specifically for rendering.
A poor CUDA graphics card may well be slower than cpu rendering

Also, the 4800 only supports version 1.3 of the CUDA specification.

You should aim for a card that supports 2.0 or higher. Some of the features that Cycles uses aren’t fully backward compatible with 1.3 cards.

Depending on what you’re scene contains, lack of CUDA 2.0 support on your card could possibly be a source of some crashes.

thank you very much. i’m going to return it and pick a gtx card