Damn that's a lot of hate for the XCR. I wonder how many have actually owned it and used it for a while and performed direct comparison with other firearms to hold such staunch negative opinions ? I'd venture that most posters are just armchair gurus who base their judgment on "extensive internet research" and “friend’s experiences”
I have owned an XCR-L for a while and have fired it extensively ~ 7000 rounds and dragged it around hell's half acre while trekking/ bag packing/ camping etc. It's been banged up, dinged around, soaked in the rain, dropped in puddles, used as a mallet to drive down tent hooks (unloaded of-course) and had all sorts of 'oh-s**t' experiences that a utility tool would be subject to while 'roughing it' and it still performs like a champ and shoots ~ 2MOA with irons (100m, 10 shot groups). It would probably do better with a scope, but I can't be bothered to go through the hassle just to satisfy internet commandos. The only failure ? The lower tube of the stock got bent slightly and was replaced by Wolverine no questions asked under warranty. It has fired when it’s dirty, wet, hot (upto +35C), cold (upto -15C) and with all sorts of crappy ammo.
In short, it works as designed and does a bang up job while doing it. It’s sound in it’s design, refined in it’s manufacturing and fit-up, robust in it’s operation, relatively maintenance free and (thx to the regulator) not picky at all with ammo. Oh, and inherently accurate to boot. What more does one really ask for in a rifle ?
To the Original Poster – I imagine the XCR-M to be quite identical to the XCR-L with the exception of the caliber of course. Pick which ammo you feel fits your useage criteria better (5.56mm NATO or 7.62mm NATO) and just go with the corresponding model. Note that both models have an option for interchangeable caliber kits– if that is a criteria. I don’t own any additional uppers, but the 7.62x39mm kit does look interesting for general plinking.
Note that as I do not hunt, I cannot advise you from that perspective. I’m sure more knowledgeable members can chime in on cartridge suitability for hunting, but would imagine that anything a small bullet can do, a bigger bullet will do better!

Any questions – ask!