Here's a build i put together for my brother-in-law yesterday. He also wanted a CAD 3D modeling build, but his budget was $1000. You could spend the extra $500 on either monitor(s), a Quadro FX1800, an i7 860, or SSD.
I had a similar needs when I was looking to build a machine. Unfortunately my budget was much less. Anyway, the research that I did showed that most of the work for CAD programs and the like are done by the cpu. And some like Pro/E will use all of the ram it can get its hands on. Your build looks good to me.
Oh yeah, I went with AMD because I had never used one. But so far I am impressed with the 965.
It's not a bad build, but the Intel chips are faster for this type of work. The 750W PSU is massive overkill and the 640GB WD is slower than the 500GB Samsung drive due to higher platter density and other optimizations.
Alright, so here is my final build. One more question though, is it worth spending all that extra money on the two velociraptor hard drivers? I would set them up in RAID 0. Would this make that big of a difference considering everything else in the build?
I would completely ditch the whole VelociRaptor idea. The Samsung F3 drives are just as fast or faster for a fraction of the price. I'm also really not a fan of the OCZ Gold RAM. Here's a very nice CAS7 G.Skill kit: