Explosion In a Spaghetti Factory – totally rubbish lol.
To be honest, I would never use m4s or x2s in the alps, but then niether would I use saints, 'the ones', or any magura brake. the only brake i would use is the tech moto with the vented disc which is what I have.
However my friend used m4s in the alps and never had a problem.
TBH my friend has slx brakes and I really like them. you can't go wrong with either the hope or the xt. It really does come down to price/looks, however like other people have said you won't be able to rebuild a shimano brake in 2 years time, but you will a hope brake.