The Oregon State University Open Source Lab is preparing to host the 2004 Beaver Challenge. This contest seeks to benchmark different open source operating systems on Dell PowerEdge 2650 servers. The challenge states:
"There will be two classes that each team will compete in. There will be a base class where everyone must follow the rules outlined below. The second class will have no rules except for the fact that every team must document all changes made to the base install."
I recommend reading the methodology to see the full rule set.
The FreeBSD-Hackers mailing list shows a call for tuners for the "unlimited" competition. There's also a FreeBSD forum at OSU. Results of the challenge will be posted for all to benefit.