Remember that Quadro cards are designed for OpenGL, not DirectX, so even if you have the top Quadro card, you'll still get miserable framerates in DirectX games (Which the vast majority are).
The only area you'll see a performance increase with a Quadro is OpenGL rendering, which most people outside of scientific research areas won't even think about doing.
Save the money and go for an X1900 (If you have enough to even consider a Quadro, this will be easily affordable).
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