I've been making 3D renders since the late 1980's. I would buy faster computers, only to have the software add more features to use up the CPU cycles. In 1990, I used to dream of how great a 1 gHz processor would be for Lightwave. (I was running at 50 mHz then on an Amiga 2000) Now we render at 3 gHz, but use larger image sizes and render billions of polys. It's cool, but I still say the software will always task the hardware heavily.