M sport is just a branding thing, mechanically they have stiffer lower suspension and standard cars came with a half leather half alcantara interior.
Clubsports are lighter, have less sound deadening, alcantara steering wheel (most have been sold/robbed), special Clubsport style split rims, black window trims, fake carbon interior and quite cool is the red speedo needles.
People "claim" the shift was different, I don't see it. I've driven CS and CI models, both with about 100k. Couldn't tell the difference.
10bhp more, 300rpm more, shorter final drive, negative front camber, stiffer front roll bar and apparently stiffer lower arm ball joints (doubt it).
I SERIOUSLY looked at getting one, and to be honest I still really want one.
Lightly stripped with some tidy buckets and a huge set of slicks...