XDM with magwell should be in the Enhanced Service Pistol division.
It gets hard to specialize and keep everything straight. For example, I compete in Stock Service Pistol in IDPA and Production in USPSA and sometime limited with my Para 2011 style .40 (and will again now that CCA fixed it). IDPA is, in general, more restrictive on modifications, types of holsters/mag pouches, etc.
But, while .40 (my limted gun) scores major in USPSA, the dimished capacity and higher recoil mean you are at a (however slight) disadvantage to the 9mm guys in 3-gun. While my production guns have less 'stuff' and since there's so little 3-gun in Iowa, I haven't built a pistol for it. Watching some of the big 3-gun shoots is interesting, mouse fart loads, large extended mags, it's very gamey, as it's supposed to be.
But, as Tim said, just go, they'll tell you what division you're in. And for me, doo-dads are not going to make a difference. If my reload takes another 1.2 seconds, it's not going to matter as I have lots of room to improve as a shooter.