I have flown the J model quite often, average gs is 150kts, doesn't like to be flown slow, power on stalls (to the break) are a little dramatic-keep the ball centered! 10 gph for gas, but beware of the lycoming 200hp fuel injected engine-I had an inflight failure on takeoff, and have several friends who had similar incidents.
As for the M model-its very fast, it vibrates a little more than the K models continental, but they are very fun @ 185 kts avg gs, 19 gph, alt. preselect, and fd.
I own a 1979 M20K231 with the continental TSIO 360 165 kts avg gs @ 12.8 gph!! Very efficient machine and cheap to operate. All mooneys that I have flown do not like to be flown slow.