Isn't the M+S marking for all season/winter tyres?
With the 'normal' tyres I found that if I use the recommended 2 people setting the middle 2 channels of the tyre wear down faster than the outer edge! I've just put 2 new fronts on mine this week which were down to 2-3mm after just under 7,000 mile
(I do a lot of stop/start trips so that doesn't help) the backs are still on 5.5mm. When I get the chance I'm going to check/drop the new ones a couple of psi below the recommended setting, 75% of journeys I'm in the car on my own anyway.
You can also use the comfort setting, but you need to keep the car in comfort mode if you do! That's the one with the information/book symbol next to it.
PS: Mine are the 18's and recommended for 2 passengers is 35psi f/32psi r and for the comfort mode is 30psi f/28psi r....so I think a happy medium for me would be 32psi f/30psi r.
After less than 7,000:
The new meat:
The outer edge difference where the coloured lines are was a shock!
Feels a lot more planted to the road now when pulling away from lights/junctions
especially since it hasn't stopped raining since I had them fitted!