I use a Quadro FX1400 in my system. Its only 128mb ram but its great with solidworks (real view etc and clean renders). They go up to an fx4000 or maybe higher now and these cost a lot £1000+. I got mine new on ebay for £100, would have been £400+ from a shop. My mate has a FX3500 I think with 512mb ram which is fab but excessive for cad, his main work is video production. If your planning a posh card for rendering it wont speed the render time up as thats down to processor power.