You wont be dissapointed in an M7, not as far as I can tell. I went from a 02 RMK 800, slp pipe can clutch, and lots of lightwieght parts to a bone stock '05 M7 153 EFI.
Yesterday I rode with 2 '02 800 RMK's both piped, one 151, one 144, a new stock 800 XP 154, and a '07 600 RMK with a 660 kit piped.
I was trading high marks all day with the XP, and that rider is 50 lbs lighter than me. Most of the time I was marking him by 20 feet.
I used to make fun of my buddies M7, not anymore. Great in the powder, and climbs better than a 700 has any right to. If you have a lot of rough trail to ride in and out, the M7 suspension isn't great, and it uses more gas than any of my buddies sleds on the same ride. For the price I think it is a way better choice than a rev. The D7 is another excellent 700, but quite a bit more $$ than the M7's.