Totally agree with this. ION systems can play 1080p content no sweat. They also are very low power, so the system is quiet.
Also, why in the world would you run XBMC under Windows?????? XBMC in Linux supports VDPAU, which is how low end stuff like the ION can play 1080p flawlessly.
If in any problem you find yourself doing an immense amount of work, the answer can be obtained by simple inspection.