Following the recent results of Hypervisor performance testing found here conducted by the teams at Virtualization Review presents the fact XenServer performed best over the largest range of categories in our tests, as you can see in Table 3 posted here
Add in the everRun Fault Tolerant capabilities to protect your applications and you have an exceptional platform for Server and Application consolidation that provides fast ROI and lower TCO.
I'm conducting POCs with SQL Server workloads running on XenServer with everRun protection and the results are impressive.
-Todd