I would chock this up as the VS compiler being much better as jacob1 said.
When i compiled tpt a while back after adding some shit to it, i was getting ~57fps on a save where with his mod i was only in the low 40s.
Unless 64 bit operations are being fudged with 32 bit ones, 64 bit will likely be slower. More data means some operations take longer, etc. It really all depends on the cpu.
Don't drop 32 bit! If the game doesn't support 32 bit, then all of the players will be gone, because most likely, they use 32 bit.
I'm going to try and get the pc version on my kindle.
x64 also has many more registers to work with, a larger instruction set, etc.
It isn't cut and dry which is more efficient, except from probably a cache perspective.
I say we only start supporting the x32 ABI and get the best of both worlds, the x64 register set and the x86 integer/pointer sizes.