Form the Stardock article:
"not because 64-bit is faster or anything like that, it's just a memory addressing thing and that's it. I don't want anyone thinking that there's some magic about it other than that you can have very very very large textures being juggled in pure RAM all the time."
The only reason 32bit code runs a little slower is because it requires emulation whereas 64bit code can run natively. DCS in its present state is not taking advantage of 64bit.