I would also like to get 64bit version of XBMC.
Reason - I prefer to use 64 bit OS.
MYTH - there is no reason to have more than 4GB of memory for HTPC.
TRUTH - Windows will use any spare memory for cache manager. With cheap memory, it's perfect way how to boost up your HDD performance actually. Read following (part about general cache manager in Windows):
http://blogs.citrix.com/2012/10/25/pvs-i...e-manager/
MYTH - there is no performance gain in using 64bit.
TRUTH - there is performance impact when using 32bit program on 64bit OS:
http://www.viva64.com/en/l/0002/
"Different processor architectures have a bit different WoW64. For example, the 64-bit Windows version developed for Intel Itanium 2 processor employs WoW64 to emulate x86 instructions. This emulation is rather resource-intensive in comparison to WoW64 for Intel 64 architecture because the system has to switch from the 64-bit mode to compatibility mode when executing 32-bit programs.
WoW64 on Intel 64 (AMD64 / x64) does not require instruction emulation. In this case the WoW64 subsystem emulates only the 32-bit environment through an additional layer between a 32-bit application and the 64-bit Windows API. In some places this layer is thin, in others a bit thicker. For an average program, you may expect 2% performance penalty because of this layer. For some programs, it can be larger. Two per cent is not very much but keep in mind that 32-bit applications work a bit slower under the 64-bit Windows than in the 32-bit environment."
I've done user load testing few times before, we've seen CPU\memory penalty of 10-30% (depending on application).