You would be best to start off with an 17t pinion with the 82 spur and then work your way up to a 19 tooth pinion. Don't go any higher than that, I don;t have any experience with a brushless, but from what I have read, gearing these are critical, it would be better to undergear (smaller pinion) than to over gear (large pinion). A 20 tooth seems to large, and you probably think to yourself you don't want to wreck anything so quickly, so be safe and stay under the 20 tooth.