From what I've been seeing on forums, etc... plus what this place sells
Their systems are overclocked by default.

They sell (800Mhz FSB chips)
2.4Ghz OC'd to 3.0Ghz
2.6Ghz OC'd to 3.25Ghz
2.8Ghz OC'd to 3.5Ghz

So my guess is those are easily acheivable overclocks (almost guaranteed and probably at default voltage) and run reasonably cool with aircooling. Plus its the right speed for them to run sync bus with PC4000 (DDR500). Seriously fast systems!! (personally I would build my own)

With good cooling and a bit more juice you can probably expect 3.5 - 3.7Ghz from all 3 of those processors.