Identifying a benchmark to compare overall performance of VM virtualization vs hardware Which performance index is most suitable to find out real performance of your VM limited by sharing and quotas?

For example, if you have a physical server with 4 cores and 16 GB RAM, its performance limit might be higher than if you have same on AWS or in some VMWare product.

How to compare to find out the gap? Is there an overall index or better to use some reference applications' performance as benchmark? (tough, though, if you still going to develop that application)
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".