Chelgrian wrote: "Windows cannot do this and requires and emulated 32 bit subsystem called WOW (Windows on Windows) which incurs a slow down. "
There is no “emulation” for 32 bit on x86-64 Windows!
Any 64bit OS offering 32bit app compatibility will require some parameter processing for 32bit OS API calls - whatever name you want to stick on it. However, this is a really minimal amount of work.
The performance impact for most 32bit apps is completely in the noise.
Even looking back almost 3 years at XP 64, the impact for games was in the 0-5 fps range, and this article is using a beta XP-64 and beta drivers. http://www.anandtech.com/showdoc.aspx?i=2085p=1
[ Aside: if you’re running on “Itanium” hardware, then there is a significant slowdown for 32bit apps, but that is another story entirely and applies to all OSs. ]
FYI - interesting tidbit: 32bit applications (compiled /3gb aware) running on 64bit Windows will have access to a full 4Gb of -virtual- address space.