I have been reading this thread and found it very helpful so I decided to register to the forum so I can share my experience as well and maybe help others decide (I still havent lol).
I am 1,82 (6 ft) and around 110kg (220), muscular build and wide shoulders. I tried the CF seat in my local dealership and found it amazing. It fit like a glove. Literally. Not too tight, not too hard not too anything. Just perfectly snug, as others have stated. Both at my legs and butt, as well as my back and upper body. However, since I am getting an M3 as my only car for daily drives, short and long trips (not really interested in track days since tracks are really scarce in my country), I was hesitant on how I would feel after a 3 hour drive, or after 2 hours stuck in traffic. I still am actually.
I was thinking of getting the regular seats because of this. I found a car at another dealership that had the regular seats and thought I should go try them. If they give me at least 70% of the feeling the CF seats gave me, I will go with the regulars. Once I got inside the car I was really dissapointed. I have started reading this thread a couple of days before I tried the regular seats and I thought the OP was exaggerating. Unfortunately, according to my experience, he wasnt. The regular seats felt terrible to me. Of course this is totally subjective. Its not a bad seat overall (obviously) but it just doesnt feel like it belongs in an M3/M4. None of the snug feeling, none of the mood that the CF seats gave to me. Just a seat. Maybe it sounds funny, but I cannot find another way to put it. Its just that. I didnt feel the support I wanted. I just sat on the seat not in the seat as another member said. Maybe its because of the lumbar support which I found a bit too much even at the most deflated setting, but I just could not feel connected to the car at all. The exact opposite to the CF seats.
I still am hesitant on what to choose because I am a bit scared of my enthusiasm since this is my first sports car (motorcycle enthusiast mainly), and the first bucket seat I have ever tried. But I am really sad the regular seats were so disappointing to me. I truly wish they werent. The choice would be a hell of a lot easier if the regular seats were a bit better (to me).
I believe you should definitely try both before ordering. The problem is that apart from getting in and out of the car (which I didnt find much of an issue to be honest), the question of how comfortable they will feel in a long trip will still remain. And thats what is killing me and I have not decided yet. Perfect fit for the 10 minutes I spent stationary in it, but no idea what happens to my back after 3 hours in it.
I would like to add 2 more parameters though since I do not remember anyone noticing them (excuse me if Im wrong)
As I said I didnt find getting in and out of the car an issue. However, it really becomes a big issue when you cannot fully open the door. In a tight parking space where the door opens only half way, it could really be an issue getting in (and especially getting out) of the car.
Another problem with the CF seats I noticed is that when you are sitting in the passenger seat, you do not know what to do with your hands
CF seats felt great while holding the steering wheel, but my girlfriend was telling me that she felt weird because the only position she found comfortable was crossing her arms in front on her chest. I laughed and thought she was exaggerating, and tried to sit on the passengers seat and found out she was right. Casually relaxing your left hand on the rest, or holding the door handle with righ hand, or whatever, just feels wrong. And that is kind of an issue too. Maybe a fake steering wheel bolted in front of the passengers seat could solve that problem
All in all, heart says CF seats, brain says regulars. But I still cannot decide.
Definitely try both of them before ordering since it is totally subjective. Stating our dimensions and all can be helpful but you should feel it for yourselves before deciding.
Sorry for the long post and I hope I might have helped a bit.