Which of the processors (i7-975 and Xeon 5680) performs best (fastest) for a workstation running mainly various flavors CAD (AutoCAD, Autodesk Architectural Desktop, etc) and 3DS Max within comparable price range? If it is the Xeon, should I go for the quad-core or six-core?
Well I wouldn't get the I7 975 when you can get the 980X for about the same price. The Xeon 5680 is not necessary unless you plan on running some crazy amount of RAM like anything over 24GB would benefit from a Xeon since when using a large amount of RAM the Xeons ECC will be needed but the Xeonl also cost a fortune my suggestion is get an I7 980X.
Thanks for the advice. I looked more closely at the 980X but I discovered that the graphics cards available for the systems on offer do not include the high-end 3D graphics cards that can make a lot of difference to CAD and architectural visualizations. Only few brand names were offering the 980X anyway, and it appears the configurations they offer are tailored for gaming and not CAD. I painfully decided to go for the more expensive Xeon 5680 hoping that the performance improvement will justify the 'skinning'.