There is a Xen vs. KVM in performance question on ServerFault.
What will be the speed difference if the choice is between Xen and OpenVZ?
Searching for such benchmarks does not show any results newer than 2008.
What would be some important performance measurements to compare OpenVZ against Xen?
Some may say "you're comparing oranges and pineapples" but I have to choose 1 of the 2 and it needs to be a wise choice. Performance is most important to us. We may switch away from OpenVZ because Xen is more ubiquitous but only if performance overhead is not significant. Next month (January 2011) I'm thinking of doing my own performance comparison - here is the project planning blog.