Without trying to sound like a broken record, I strongly recommend RHEV and/or RHEL AP. Both include unlimited virtualisation CPUs and guests for no extra cost. For your premium 24x7 support, that's $2500 per physical host per year, and all your RHEL guests are free (and also fully supported 24x7). Plus RedHat are keen as mustard to get more RHEV customers on board. They'll happily throw dedicated engineers your way to make it work. We're migrating a tonne of workload from HP-UX (physical for PROD, HP IVM for all other environments) across to RHEV/RHEL. It's been a nearly trivial task, and the performance is brilliant. RedHat's support in the whole affair has been equally fantastic. And if you just want to try it out for $0, you can always to a proof-of-tech on CentOS.