With SU, the division of work goes so that the CPU takes care of the vector stuff, and the video card of textures, shadows and the like. So in fact SU is very CPU-intensive. With other apps, it might be different. Video card performance generally only affects what you see on screen and how responsive your apps feel. Rendering to a file is typically done by the CPU only, the video is used to draw the user interface and preview windows etc. on the screen.

As SU, like most modeling and CAD applications, is still unable to profit from multiple CPU-s, buying a new computer with a dual-core or multicore CPU is not a great way of enhancing SU performance. Many rendering applications, however, can split their tasks between multiple processor cores.

Anssi