I ran Allegro 16.5 on RHEL 5 Linux with no issues, I'm currently running 16.6 on RHEL 6 but I'm having issues with our team supporting the newer level of Cadence/Allegro. So as a counter measure to that I've been running 16.5 on the KVM for windows 7. I wish Cadence supported 16.5 on RHEL 6 so I wouldn't have to do this.