I prefer the MS for longer journeys. It goes like a rocket in a straight line, wallows on the bends. I find it very comfortable on long journeys (e.g. UK to the Alps). M3 is like a hot hatch, very tight. MY lacks that precision
Unless you want to corner on two wheels, like you did 50 years ago
, the MS might be better.
Its a big car (tight spirals in multi-storeys, narrow country lanes, width restriction bollards and parking in general). its very low to get in and out of; my 80's relation prefers MY, happy with M3 but the MS he finds somewhat difficult.
If you are going "long distance" you might want to try
ABetterRoutePlanner to see how much difference the MS75 and M3/MY LR (or M3 SR+) would make. (You can choose car model, and then Start/End of journey, and any waypoints, and it will calculate where you will need to stop to charge; makes it easy to compared Brands / Models.)
Basically you need, say, 30 miles contingency, and you will ideally only Supercharge to 70-80%. For a drive-charge-drive-charge the charges will only be 60%-ish of max real-world Motorway range.