Good Calculator For Gearing..

If you're into swapping sprockets around here's a good site:

http://www.gearingcommander.com/

Just type in your bike & press 'load presets' then mess around with sprocket sizes.

As well as a speed chart as shown below there's charts for:
Top speed per gear for 49 sprocket combinations
RPM deviation due to drive train changes
Chain geometry changes due to sprocket & chain changes
Relative sprocket & chain wear due to drive train changes

Throwing some figures around for a DRZ400.

Excellent little site - thanks for the link