You really need something like an Intel Core i7 with 16gb DDR3 1333 ram, and some sort of Nvidia card that supports CUDA. If this is a pure editing rig, the highest end Quadro card you can afford will help.
If this is a combo editing/gaming rig, the a minimum Nvidia GTX 560 Ti card would be nice, with the 570 even better. Even then, 3D editing is tough. Many of the pros are using dual 6 core Intel Xeon CPUs, 32gb ram, and a Quadro 4000 card. I'll let you look those up for the sticker shock.