This doesn't appear to be universally true. We've run 4.1.4 with Windows 7 64bit on top of CentOS 6 and not seen any noticeable performance problems. The way you describe it makes me think it's not the sort of thing we could not notice if it was happening. This was Windows 7 Enterprise as opposed to a server OS guest.
Same, Its obviously related to host os and hardware. As I sit here over lunch manually fixing another snap shot debacle in 4.1.4... Sigh...
jlc