I've a set of all season on at the moment, I can't really tell the difference as a, they've been on car since I got her. B, not driven awd cars before and c, I don't drive the car like my old rwd so not really a help.
In mud they seem to clear a little better and as for snow I couldn't tell you.
Problem I have is that pretty much all the recommended tyres Form mine are xl which tent to be m&s rated too. From what I can work out is that the compound is only slightly different to summer rubber but no where near as good as a dedicated winter compound.
As for wear I don't seem to stress them much and they haven't worn much at all, in fact they need changing due to age not wear