Which CPUs support VT-x

Yes, database operations usually have to be written to the disk before they return as successful. This is a very good thing, as a program shouldn't continue before knowing if the operation was done properly. If you would parallelize your test program, you would likely find that your loops have less impact on the runtime, as the loops could be run while other threads are waiting for their IO operations to finish.

Also, while certainly modern CPU's are the most unlike candidates for being the bottleneck in a database, this is not generally true: Depending on your application and it's DB queries, they can be extremely taxing on the CPU, leaving the disk subsystem idling while the CPU is running at 100%.

It's quite simple really. For homogeneous clusters and single host setups use the host option. For mixed clusters, use the lowest available CPU version, so if one host is Penryn and the other Nehalem, use Penryn on both.

If you are using RHEV or oVirt, this is already built in. VMWare have this called "EVC" and position it as a huge feature.

Getting back to performance, you definitely need virtio everywhere you can put it. And if you still hit performance bottlenecks, those can usually be addressed on a case per case basis, depending on where they occur.

[offtop]On your choice of distribution I have already commented in another thread[/offtop]