Unsolved problems in web load testing

Web load testing is getting more attention in web development field. I would like to know more on the recent researches on web load testing for different web platforms. Are their any unsolved problems on web load testing on different web platforms? Does the web platform effect the performance of the web application? Does the web load testing tools result differ while performing in different platforms?

At last, can i perform an evaluation of different web load testing tools for different cloud or web platform and find interpret the results forming a conclusion for my research?

I would like to know more about web load testing. Where can I start and where to find the problem domain.

Many thanks