I typed my post a little bit on the tired side. Basicly what I am trying to say with the spring swap is its not as scary as people make it sound. I waited roughly a year before cracking my mechbox open but when I finaly got the nerve to do it I went "this is what people are scared of? its just some springs and gears and moving parts....* mind you I do have a mechanical and IT background....
If you do end up getting a TM with a stock gear box, if you want to bump the FPS up just be warned that you do have to change the bushings out from nylon. Heavier spring causes more friction... friction causes heat.... plastic VS heat, heat wins.
*btw some fields do require the hop up to be off for crony.*