ZDNet Clock is a software tool you can use to overclock your Mac Pro (or XServe’s, if you’ve got ‘em).

“The improvement in performance is quite remarkable. For example, the cheapest Mac Pro in the current series with a 2.80 GHz processor runs significantly faster after overclocking than the most expensive at 3.20 GHz. This is because in addition to the CPU frequency, the main memory clock speed is also increased, which results in an additional increase in speed. The price difference between these two machines is 1430 Euros.

ZDNet plays it safe when overclocking. ZDNet Clock does not use any voltage increase for the CPU, the front-side bus (FSB) or the memory modules. Voltage increase leads in increased electro-erosion and shortens the life of the modules in question. In order to designate an overclocking trial as stable in the ZDNet test, the computer has to perform the mprime torture test for 24 hours without any errors. And in addition to this, there must not be any reports of ECC errors from the FB-DIMM main memory modules.”

At this point I’d say proceed with extreme caution if you cannot afford to replace your Mac Pro should it all go sour…but if you are sufficiently interested, you can download ZDNet Clock here. More info on adverse side effects and such here.