With all due respect to Dan S and RGS you're better off in Production.
A M&P 40 is a very competitive Production gun. If you reload, load minor. If you don't reload, shoot a light load, like Wolff. The larger diameter of the 40 will give you an extra point or two on a perf shot over 9mm and you won't wrestle with the gun as much. Theoretically you can focus more on the match, as opposed to shooting mechanics (nothing wrong with mechanics - but there will be a lot to take in at the match Sunday). Shoot Production, it's competitive locally and nationally so you can gauge your performance.
As far as Limited 10 is concerned (I'll put my helmet on here); At big matches you'll get your butt kicked by guys shooting SV and STI Limited guns loading 10 rounds. In the 2007 Limited 10 Nationals, 7 of the top ten shot SV/STI platforms. The M&P is not the desired competitive platform in Limited 10 (at least at major matches ). BJ Norris is considered one of the best up-and- coming USPSA shooters; He shoots a M&P - in Production. He's shot Open division the last five years.
Additionally; The M&P shot minor will also allow you to use identical equipment (pistol, holster, mags, ammo, etc.) in IDPA for SSP (Stock Service Pistol). There is no major power factor in IDPA for 40S&W (and that's a whole 'nother story). SSP fields the most shooters at a given match in IDPA. As oppossed to Limited 10, the M&P is a very competitive platform in this division.