I honestly can't really answer that question for you, especially since I haven't owned an M-Performance vehicle, but only a full on M, but I would think they are similar.
I'm a steering snob so my definition of normal can't really apply to any modern BMW as my normal is hydraulic steering with road feel, but no BMW really offers either of those things. Since you haven't owned a BMW before electric steering, your normal and mine are likely very different.
I have only had 2 modern EPAS BMW's, a 540i which I really disliked, it was incredibly boring and the steering was awful no matter mode it was in, and an M2. Honestly the 5 series was the reason I left BMW for the first time in 20 years, my CLS honestly has better steering feel than my M2, of course nothing compared to my son's X3 which has hydraulic.
Anyways, in the M2 I prefer comfort steering. That is because it adds a bit of assist without being too much, and feels quicker and more precise than sport, which has increased effort and in my opinion feels slower in responsiveness/its ratio. Comfort steering gives it a more nimble feel that I would expect of a small wheelbase sports coupe despite the name suggesting otherwise. That is my "normal" but like I said, I still prefer my CLS's steering, or even that of a Mazda. Now I don't own an M340i, but I would expect that the steering rack acts in the same way regarding steering modes.
That probably didn't answer your question, but hopefully you found a mode that works for you!
