If your local hobby shop can get the Hitec 645 they should be able to get the 985 Hitec. As far as an improvement over your stock servo I have no idea what the specifications on it is do you? More then likely will be better but not best. If all you do is bash it will be OK? Sorry I have gotten use to good servos and will never go back to inferior ones. So it is all up to you.
You are welcome.