The question of which CPU to use for 3D is very dependant on the application being used and whether the app uses SSE2 instructions or is multi-threaded. For instance Lightwave is multi-threaded and uses SSE2 so it usually runs best on a P4. Apps which use SSE2 will generally run faster on P4 or AMD64 processors. Apps which don't use SSE instructions (i.e. Terragen) will generally run fastest on an AMD athlon with the highest clock speed. I'd suggest asking about CPU's on the fora for the applications you use to see what people recommend. More RAM is a good investment as not having enough will cause the system to use virtual RAM (the page/swap file)on the hard disk which will slow any application more than a slightly slower CPU.