depends on whether jcl optimizes/has his code optimized with sse instructions. engines don't need much of an integer arithmetic, it's the vector and floating point instructions that count. the most part of these run in the directx libraries (there are two sets of them in 64 bit windows, one for 32 bit and one for 64 bit as far as i can remember). of course you won't see a speed up of rendering itself since the graphics card is independent from the cpu. but stuff like mesh loading, bitmap conversion, level compilation etc. will definitely run faster (if optimized).
