Sye,
Go to this website - calculates the effects of all gearing changes for YOUR bike.
http://www.xs4all.nl/~ator0437/gc/ It is great fun as well - see what sprox you need for a 260mph top-end!!
BTW - remember, a 14 tooth from sprocket will put a lot mor strain on your drive chain. Plenty of people do it, but then plenty of people snap chains.
Spin