Rendering apps are one thing, and CAD programs are another.
As far as 3DS max goes more of everything is better, more CPU power, more graphics, memory... but if you look at it from a PRO-E or AutoCAD point of view its not that much of a difference. If you put an 8-core or a 12-core CPU on a CAD/CAM rig you won't see much of a difference to a quad core, even a dual core rig.

And i wouldn't really put 3ds max or cinebench into the CAD group... that's reserved for programs that actually have some practical use, not just making pretty 3d models.

Basically, wait for the i5 release and then you'll know. I don't see how anyone can tell you which will be faster since one isn't even released yet.