Identifying a benchmark to compare overall performance of VM virtualization vs hardware
You should do a comparison of commercial virtualization products on the same hardware resources, OR benchmarking commercial virtualization products individually, there are ways to do it, you can even script it.

For example, VMmark is a free tool used to measure the performance and scalability of virtualization platforms VMmark

Since your question is very generic, you should clarify real performance, overall performance. It might mean "real performance in virtualization".