MDM vs DSC-off at Laguna Seca, Infineon and Thunderhill
Based on my experiments at these specific tracks (the only ones I have been on anyway) here is what I have observed:
Laguna Seca: MDM is generally not intrusive except at turn 6 and turn 1. In these 2 cases the DSC light comes on even though it does not seem necessary. At these turns with DSC off the car is perfectly happy at the same speed. My guess is that at turn 6 the bump throws MDM off and at turn 1 the speed of 100+ mph and slight drop does the same. At turn 6 MDM kills the power needed to accelerate out of the corner. I haven't done a lap time comparison between the 2 as I drive with DSC off, but MDM does pretty well for what it is. It even allows mild oversteer at the other turns before it kicks in.
Infineon: A similar story here. MDM comes on for no good reason at turn 1 (100+ mph turn) and turn 6 (carousel, high g 70mph turn). With DSC off at the same speeds at the same turns the car is just fine. MDM of course does not allow you to drift around turn 7 (a safe place to do so) but is still allows for mild oversteer to develop.
Thunderhill: MDM incorrectly comes on at turn 8 which is a very high speed turn and stays put otherwise. It never comes on for example at turn 2, which is a very long left hand turn, unless prdovoked.
In all the above cases I described, when driving with DSC off the car is totally happy and MDM comes on incorrectly. So I think the car can still be enjoyed with MDM on, unless you want to oversteer for fun or doing time trials.
Keep in mind that even with DSC off the car is very predictable and never abrupt provided the driver stays concentrated on the road. I have had minor tank slappers occasionally when I found myself thinking about stupid things while driving on track with DSC off.
Of course DSC fully on is way to intrusive. I am reminded of this when I forget to push the M button that has my preferred settings: (Steering: Sport; EDC: Sport; Throttle: Normal; DSC=OFF; S4 or S5 depending on mood).
I hope the can help you choose for yourself.
Stock everything M3 with stock 18' tire sizes (RS-3 or RE-11). Advanced group driver.