rendering is mainly done by the cpu, best thing to do would probably buy an asus z7s workstation board(review of sorts) otherwise something with an i7 socket, and have hyper threading on, best graphics card you could have, would be something out of the quadro series
I ran AutoCAD and Solidworks on my 8800GT and 2.6 Dual core and it works perfectly. Granted, it probably doesn't perform as well as a workstation card but it runs fine for the money. Quadros are too expensive.