Performance Shootout: Vista 32-bit versus Vista 64-bit

From the article: Even the 3ds Max 9 and POV-Ray rendering tests seem slower in 64-bit mode.

Rendering using many instances of many data structures. This requires a large number of address pointers. When you move from a 32 bit environment to a 64 bit environment, those pointers grow from four bytes to eight byte each. That can reduce the effectiveness of a processor cache by 15% or more. Switch to 64 bit only if you're squeezed.