Engine is an animal with shocking capabilities..... blah blah blah! I don't think it's going to be much different than the 1M engine with a proper tune on it. The torque will be the most fun, but if someone has not driven a 1M with a tune on it then it will be loads of new fun compared to an E9x M3. The day to day driving of the 1M is just overall more fun than a E9x M3. It's the torque that makes you drive with a constant smile.
The only difference that I am hoping for is that the torque is there at all times on the track for the new M3/4. With the 1M it can kind of come on quick and keeps you on your toes. If the torque delivery is slightly smoother, then we have some improvements over a tuned 1M engine. Just my thoughts.
At any rate, I'm looking forward to the real life comparison!