I've built a lot of open division raceguns and here's what you will be up against in that division.
The gun itself will be compensated to the point that recoil is almost nonexistant, the dot in the scope will not move from the target, as a matter of fact it will move very little at all in a properly set up racegun.
Most open division shooters will be using mags "big Stcks" that hold a large amount of ammo so if the M&P mags are not 30 rounders you will be at a disavantage as for having to make mag changes.
I you want to be a serious competitor in USPSA open division I believe you will be better served using an open division racegun.
Best Regards
Bob Hunter
www.huntercustoms.com