What type competition are you considering.
There are different competative systems in use around the country that typicaly have class structures which provide for different hardware to be used.
Our local club holds IPSC/USPSA shoots which allow the XDM. Magazine capacity and sighting system can dictate which "Class" you would compete in but you would certainly be welcome to compete.
We have one participant that has been competing since 9 or 10 years old. He's damn good also and kicks this old guy's backside regularly.
Use your computer search and review USPSA and or IDPA responses.
There is a lot out there for those interested.
Have fun while you are at it.
PS: I use the M&P40 but 2 years back used an XD40. Either is a good machine.