actually they are exactly the same, but the M7 has a longer track. The same SLA suspention, same front chasis, same steering angles, same front suspention travel...i could go on but i think you get the point. The only difference between the two is the track design.
Ive seen more AC sleds broken on the side of trails/powder pits/ ditches/fields/hills then any other sled out there. I don't trust suzuki engines for shit since i have no idea where they do their cold wether testing. Ohh and i really really really don't believe you about the ski-doos overheating. Especailly the v-twins, the EFI engines, or the liquid cool engines.
AC does have some great ideas like their ethanol mode on the firecats, their turbo 4 stroke, and their looks ( they do look sick). But i would never trust one in a million years.
Ive ridden everything from ski-doo summit X, their 800 HO, the pre-rev summits, MXZ, and MACH Z. Ive also ridden polaris RMK 900, the Fusion 900, XC 700, Classic 600, yamaha mountain max, mountain viper, RX-1. Ski doo just have it right, they know what a sledneck wants in his snowmobile on the trail/mountain/ditch/etc.
The true answer to this thread is to buy a sled, any sled and pump it up with aftermarket parts. Yamaha has the most after market parts out there, and their viper is a prime platform if you cut a few pounds off of it.