I'd make sure you do a few test drives before you make the jump. I made the jump from a 135i as well and to be honest the M3 "felt" slower than my Dinan-tuned 135i. In reality I they were really close in straight-line performance. Torque is deceptive. If you just want the car to go/feel faster, I'd just go with a tune. Go with Dinan if you are worried about warranty issues. I'm pretty positive you'll be extremely happy with the power.
2011.5 E92 M3 6MT / 45,000+ miles / 3400lbs with no driver, half tank / M3 GTS Aero, Rear Seat Delete, Half Cage • Schroth 6 Point Harness • Recaro Profi • 18" BBS FI / 18" TE37SL Black Edition • Ohlins RT • Vorshlag Camber Plates • Brembo 380GT • Endless Pads • Akrapovic Evo • RD Sport Sways • ESS Tune • Supercharger Delete (1:42 @ Laguna Seca, 2:09 @ Thunderhill, 1:56 @ Infineon)