Hey Francis, I'd like to take a stab at replying to your post and give you a bit of a different perspective. I too have just started tracking an e92 M3 and have been to Thill. I've done two events with the Cyclone, and one with the bypass. My car is stock, except for pads. My very first day, I got down into the 2:21s. The second day, it was down to the 2:12s with lots of 13s, 14s and 15s.
There are may ways to measure one's driving, but isn't time the universal yardstick? I use Harry's, and the lap data is very helpful to me in understanding what I did right and what I did wrong--and a way to know what skills I need to improve upon. Although I enjoy chasing (and passing) much faster cars, my ultimate goal is improving my own time. I guess I see smoothness more as a skill to develop, not an end goal.