Hmmm, 64 bit code is a little larger than 32 bit code (for AMD64 vs x86) as there is a prefix byte for 64-bit instructions. On the other hand the extra registers in AMD64 often counteract this ...

Transitioning from 32-bit to 64-bit can seem daunting, but it's easier than porting from a 16-bit application to a 32-bit application.