+1 for 15/47.

A lot less of a struggle against head winds plus short shifting from the lights is a right giggle. Roll on acceleration from 5000 rpm is greatly improved and still get 60+mpg. Been thrashing my Ten a fair bit the last couple of weeks on M25/A3 (5500rpm) and still achieved 230 miles before reserve a number of times.

Although it may be easier to change the front sprocket I'd recommend changing just the rear as a larger sprocket helps spread the load on the chain.