Also, you may have misunderstood. I believe - I'm not sure - that it-s not the 64-bit of W7 that allows you to run in XP mode: it's a facility under W7 Professional, Ultimate or Enterprise. Plus: I don't believe you need an XP licence to run XP mode. Beyond that, you're not getting the full functionality of XP - merely a runtime environment that emulates XP for software (and not all software) that won't run on W7. And, as Jock1e rightly says - why on earth would you want both 32-bit and 64-bit?
Sniper Elite 4 review: Headshotting Nazis has never felt so good