I've just compiled a large map on both x86 and x64 versions.
x86 --
CSG: 14.67 seconds elapsed
BSP: 6.34 seconds elapsed
VIS: 5550.31 seconds elapsed [1h 32m 30s]
RAD: 1257.22 seconds elapsed [20m 57s]
x64 --
CSG: 5.63 seconds elapsed
BSP: 3.95 seconds elapsed
VIS: 4421.16 seconds elapsed [1h 13m 41s]
RAD: 1018.92 seconds elapsed [16m 58s]
Looks like some improvement there
I've also been modifying the compilers, and so far successfully compiled a map with more leaves than the default 8192 limit (now 32767).
One query I have is why does compiling for x64 give me a warning "unknown option, ignoring: /ARCH:SSE2" when x86 doesn't... does x64 make use of SSE2 already or something?
[Edit] ^ never mind, discovered that the Microsoft C++ compiler can't compile a 64-bit program WITHOUT using SSE2. Makes sense seeing as pretty much any AMD64 based processor includes the SSE2 instruction set.