6000kv 5.5 turn motor and 4600kv

[jim76]

just keep your spur gear and work out the correct pinion. changing the spur by 2 teeth isn't going to make a huge difference for bashing. You are better to have a range of 4-5 pinions than a few different spur gears

Just do as James says, and find the pinion that will give you a ratio between 9.5 and 10, and then stick with it.