WRHapi uses quite efficient Java NIO package for its custom request processing; it is not based on Servlet API. The WRHapi is currently a project on BerliOS, it also is used by one Jena subproject (displaying temporal changes of an RDF graph).
Consider doing a simple Web application, which displays portions of a simple text file - the file contains table with contacts (person's name, address, phone); it displays list of the persons and allows to view each person in detail. See https://developer.berlios.de/svn/?group_id=7958 to download "WRHapi" server or ask Kalvis, who has a version of the source code.
For a load test, ask for a full list of contacts and then request in a random order e.g. 1000 contacts (possibly with repetitions). Measure the time spent by WRHapi and Tomcat and compare the results. Load tests can be implemented with Selenium, JMeter or any other load testing framework of your choice (it should support many (multithreaded) HTTP requests.