Autobox consistency at play there, also makes better tv. Most importantly don't forget potential, we have a smart full lock differential, and the wheel arches to run much larger tires. With a $500 chip they'll both have the same power but the 1m's ability to put that that power down in a variety of conditions is superior, I run a few mods that give quite a bit more power, jb4 g5, fill it with e85, and to a lesser extent an intake and midpipes, an extra 150hp, what could an m135i due with that power? I run 295's in the back with no rubbing and the power overwhelms the tires if I don't limit boost in the low gears, no hope for the m135i; I'm beyond happy with our cars.
BSM 1M, JB4 G5 ISO, DCI, N55 Mid Pipes, Evolve Race Midpipe Back Exhaust, Stett CP w/ Tial BOV, H&R Springs, CDV, Performance Steering Wheel, Huge Tires.