I'm safely back from my ring and Spa trip and gave all three modes (on, off, M Track) a good testing. My car is standard except for Eibachs with Conti Sport 3s all round, standard road tyre pressures, running more negative front camber.
I don't know the Nordschleife well having only ever visited half a dozen times and only ever complete one or two laps each time (there to enjoy the atmosphere and experience). I got in one lap only on Sunday evening before it started raining (delays at Dover stopped me getting out on Friday evenings TF session). I left the DSC on for the complete lap and it wasn't intrusive as I was driving well below the cars limits, mostly held up by a UK Hayabusa who was keen on taking the racing line at every corner, nearly tipping in to faster traffic before seeing them at the last minute!
The Lotus On Track Spa trackday on Monday was wet almost all day and immediately followed the 24 hour race, with plenty of fluids spillt at certain corners (La Source was awash with diesel until rain washed it away slowly). I've driven Spa plenty of times before, but not for 10 years. To begin with I left the DSC on with the occasional flashing dash light giving a helpful indication where there was a real lack of grip. Having never driven a car on track with any kind of safety system I wasn't about to rely on it, but I was impressed with how it gave piece of mind and confidence, particularly for my wife when she drove. As I got to know the car a little better I tentatively tried M Track mode, pushing on a little through the bus stop and La Source, where speeds are slow and risk of car to barrier contact are lower! It's brilliant, allowing just a little opposite lock and some wheel spin before a soft amount of electronic control is felt and you are off down the track again. I soon found this produced a better lap time (by seat of the pants feel). With DSC on the power was cutting for the first half of the start/finish straight, each time you crossed the painted grid lines; with M track on it just kept accelerating with no detectable wheelspin at the same place.
The pace of the Z4M was excellent in the wet, faster than many of the lighter Lotus, some of which I put down to confidence that you could drive that bit closer to the cars limits in the slippery conditions. Having driven and raced Caterham and Elise for the last 10 years I did feel sorry for them! With passengers I was happy to turn it all off and have a play on some of the corners, great fun, but not as fast of course. Having come across a badly damaged Elise at Raddillon and knowing that we wanted to bring the car back in one piece we kept Mtrack on for pretty much the rest of the day until the last hour when the surface dried. With the kerbs and white lines still slippery we drove with caution and avoided any spins. A continental Z4M Coupe owner was there (black, CSLs, tan interior) and didn't know you could add this software, droving the whole day with DSC on afaik, still he had a good day from what I could see.
So to sum up, M track is worth having IMO for both the road and track, particularly in the wet BUT I can see that it could become too easy to rely on it and become lazy, expecting the car to sort out your mistakes (which it seems capable of doing). I like the way M Track allows trail braking and a degree of turn in and exit angle, intruding softly if needed. So, I will likely keep it on whilst on the road or on a wet, high speed track but off when on a more forgiving circuit or almost anywhere in the dry. I'll save my other observations about the car one week into ownership on a separate thread.
Once I have some time next week I will attempt to show by video the differences between all three modes at the same piece of the track.
Cheers, Dave