Some Question from a BL noob

Hi all,
I am new to brushless...and considering converting my Revo. After reading some thread. I still have some questions.

Do you use the stock spur gear? Or do you switch to a different pitch.
I am considering getting a 8xl and a mamba ESC with 2 lipo pack. I noticed most motors have 5mm shafts. Where do you buy the pinions? RC Monster seems to be out of stock on pinions. And what gear ratio do you guys run. I do mostly bashing. Hoping to do some high speed runs down the street :017: