Well having been fed up with a reoccurring problem that nobody could locate an easy fix to gave me reason to nuke MCE 2k5 and replace with a shiney new edition of XP Professional x64.
Well there appears to be a slight speed boast (Booting is around a minute from a cold start to the desktop). Applications do appear to be more responsive. I keep hedging because any clean OS install will be faster than the previous base. I am only about 15 hours into the setup. A lot of tweaking and configuring left.
However there are a few gotchas:
Software that won't install/or work properly:
Hardware that lacks driver support
I am going to fire up a few games most notably the Unreal Tournament 2004 and Far-Cry with the x64 enhancements to see what carnage they cause.