An independent researcher (SaltwaterC) has done a performance test on several PHP frameworks / CMSes and webservers, including Hiawatha. Although speed was never my highest priority while developing Hiawatha, I always did my best to make Hiawatha fast. And according to the results of this research, Hiawatha is doing quite well in terms of speed and performance.
The results of this research can be found in this document: PHP_web_serving_study.pdf.
and how others can do better with so many developers !