I own both a 335xi and a 1M. The 335xi is tuned and the 1M is stock (aside from a midpipe).
Although they share the N54, throttle response in the 1M is substantially better (different fly wheel and different engine management software) although not in the same league as the M3. The 1M feels agile and lively to drive, and sometimes a little scary (if you turn DTC all the way off). Steering feel and precision much better with 1M, although some might find it a bit too light for their liking. Everytime I get back in the 335xi I immediately notice the car's greater mass and the much heavier steering.
I have driven an e92 M3 with DTC. The S65 is incredible as the revs reach higher and higher. That being said, I prefer the driving dynamics of the 1M (I am biased of course
). The shorter wheel base really makes the car very fun to drive.