I have back problems, and I don't get back pains from driving the M
I did in my 335i (coils stiffest setting with sways...no duh), I do in the Z4, and I do in all the Porsches
But I don't in a C63
Though it does hug me too much ... maybe I need to lose some weight
I think the m3 is very comfortable, and with the ability to put it into Sport and tighten the seats, it's golden.
I do wish the M3 had those fill in seats that the E63 has though