Someone on another forum asked me to compare the 1M to the M3. Here is what I posted.
1M is very friendly to drive as a daily driver, which is what I use it for. Also it does great on long road trips. However hit the M button and you now have a car that is like a kid jacked up on too much sugar. While she is controllable, you can tell it has a short wheelbase and wants to just maul every corner you throw at it.
My M3 in its current configuration feels tame and docile compared to the adjudicated 1M. This by no means I am saying it is a slouch. The M3 feels more like an extension of what you are thinking. In addition, when you hit sport and the intake flap start opening sooner it is like a angry beast shouting "MOOOOVVEEEEEE" at everyone. In the corners, it feels more composed with the only complaint is the DSC kicks in a little too soon.
Both are M cars and at least to me have the motorsport heritage. The 1M definitely was BMW saying to the enthusiasts crowd, "Yes we can still make these cars, so shut it". As one of my buddies who drove it said, this is what the current E9X M3 should have felt like. (He had 2 by the way).
The M3 you can tell was BMW giving the US a car that was equal to what was in Europe. You can feel the translation of all the little quirks into the car the race developers had. I am E46 M3 bias but it feel the car has a lot more soul than modern cars accept the 1M. That car has one as well.
1M is a boosted car and with a little tweaking, you get 450hp easy. The car does not need more power unless you are our drag racing other cars. The power it has for the track and street is more than enough to melt tires and have a grin from ear to ear.
In order to get my M3 to the same level as the 1M it took money. A stock E46 M3 to me seems tame and restrained. Almost like BMW said "down simba" as it whipped the lion into shape. Probably why they made the CSL to let the lion out to go maul a few Audi's and Porsche's. With all the changes I have done I feel the car is what it should have been from the factory. While not as fast in a straight as the 1M it does have no issue in the twisty back roads.