Win2k3 can run HL1 servers at up to 500 FPS. Orangebox servers run at half this because of Valve's recent interim change to the way FPS works in that engine: viewtopic.php?f=44&t=5473
Win2k8 / Win2k8 R2 with HPET enabled doubles these numbers.
srcdsfpsboost.exe is no longer needed for Orangebox games, as Valve flips the switch to cause the same functionality. It is still needed for HL1, and the numbers above assume you are running it. On a managed server, we do.