First off, are you an adult? If the answer is yes, then you should be able to make your own informed decision about buyiing a 40K+ used car and not rely on random people on the internet.. Sounds crazy when you think about it no?
Secondly, mod the 135. You seem to want an M3 just b/c it's an M. If you think this car is much faster you're wrong. The 135 is easier to mod and much cheaper to boot. Also the car makes much more torque and in city driivng will feel much faster than the M3 which need to rev to make power. Give the 135 a chance, do some mods, and then if you want traded it in. You're gonna lose money right away trading the car.