[Metallover]

Look at other revo setups like yours and see what they are geared. I would go with what BL boy said, get a larger spur.

You need to imagine every tooth you change on a spur as 1 "gear point" and every tooth on a pinion as 2 "gear points". Change the spur because it will change the final drive less.

Also, you probably already know this, but bigger pinion/smaller spur = less acceleration/more top speed. Smaller pinion/bigger spur = more acceleration/less top speed.