OpenGL has become an important gaming feature, and, I get the impression, the dirty secret of the hardware world is that the last couple of generations of gaming cards can adequately handle your CAD programs. Autodesk, 3DSMax, and Rhino all operate just fine on an X800 and up on the ATI side...and the 8800 series has really solidified the support on the nVidia side.
Check out your app's site for more info about compatibility, but I think you'd be VERY happy with the GTX, especially for half to a third the price of the Quadro FX5400 (which is also G80-based).