I don't know if you would notice a difference between any of the steel ball bearings in a mini. If you went to the expensive ceramics, you would see a reduction in weight.

I don't know if you can find an advantage per se... there's likely very little left that someone hasn't a;ready tried or done.

I'd suggest water dipping the motor (not for long!!)

and spending a lot of time on setup. Check out the tamiyausa website for their build up of an M03L.