Yeah.. Xen paravirtualized mmu is fast, and in some (many) cases beats CPU hardware virtualized mmu.
KVM has 'pvmmu' aswell, but it's not as good, so KVM is faster with CPU hardware virtualization. But that's a problem of KVM only, they haven't managed to optimize the pvmmu. And they're going to drop it altogether.
KVM people tend to say 'paravirtualized mmu is slow', but they just mean KVM implementation of it sucks :)
-- Pasi
I haven't tested or seen any benchmarks but I wonder how much the addition of a page table for virtualized guests will help. Not to mention newer features like a virtualized task priority register and ASID could continue to require less paravirt code in the guest. I get my two new 5500 series servers in a few weeks so I'm pretty excited to see some of the second gen hardware virtualization assist features in action.