I got a chance to drive a 1M a few weeks ago and was surprised in 2 ways.
1.It IS very fast off the line. I mean I knew it was going to be but SO much faster feeling than the e46 M3 which has the same HP rating. It also felt just as quick off the line as the e9x m3.
2.The part I suspected but was still surprised at how much a factor it was, is the delivery of the power and how that changed the enjoyment of the car. Nobody that has driven both and who likes a motorsport-like engine, could say the 1M is more "fun." The torque was boring IMO as it was just like a TON of cars on the road. The m3 just is a totally different feeling and only driving one can really describe it so those who have owned or driven one know exactly what I am talking about.
It basically boils down to
1.The m3 looks so much better and few can really argue this although there will always be some outliers
2.The engine in the m3 feels like a race car, sounds like a car and is flat out FUN to drive if you are someone who wants the F1 "feel" or as close as you can get.
The 1m is probably as fast or faster on many circuits and on daily driving but to me and many that really means nothing at all. The driving experience is about enjoyment and the smile it brings. The m3 can bring a bigger smile than the 1m for the reasons mentioned and that is what it simply boils down to.
I mean a Jeep SRT8 can out accelerate an M3 or a 1M but does that mean we all jump into one? Again nothing else feels like the m3 whereas tons of high torque cars feel like the 1M.