I am currently running X3e x64 under Lion-Bootcamp very successfully... If you have a copy of Windows 7 Pro it's a few hours work at most to get Sonar up and running... And if you have a dual processor, Sonar recognizes and uses both... I've got dual Xeon quads for 8 core total...
It seems most successful if you use separate actual drives (not a partitioned single drive) and a minimum of Lion and Win7 Pro... I use 3 drives right now. One for OSX, another for Win7Pro, and a third formatted for win7 and used for audio. You won't have real access to the Mac drive when in Windows...
Keni