Win7-64 can run in demo mode for several weeks iirc which is enough to check if it helps. IIRC you can reinstall it again many times to prolong your trial if it was not enough to make a decision.
Multiple reports are saying WinXP-32 causes crushes in CloD which disappear after installation of Win7-64.
I think XP support will be discontinued in Battle of Moscow as XP is not supported in modern games any more. E.g. Vista is stated in minimum spec for Battlefield3 and Win7-
64 as recommended
http://bf3blog.com/battlefield-3-system-requirements/
Same for ArmA 3
http://www.pcgamer.com/2011/05/19/ar...ents-revealed/
You can install Win7-64 demo as a second OS only for CloD.