Memory and '64bit math' aren't really the drivers here, 64bit archs generally have a lot more registers and allow better packing of SIMD instructions. Both can

Memory and '64bit math' aren't really the drivers here, 64bit archs generally have a lot more registers and allow better packing of SIMD instructions. Both can give large performance increases, particularly the later when a lot of what you plan to use that power for are things like image manipulation.