Make sure you get the right length chain if you are increasing the sprocket size.

I changed my gearing from 17/42 to 15/44 so it is much cleaner out of corners and is better on acceleration (Cadwell, Oulton Park etc) but I lost about 12mph on the top end. Having said that the best top speed I have had on track was 148mph on the Revit Straight at Snetterton so it doesn't really matter.