I just cleaned one of my MPX' this past weekend for the first time in maybe 2500 rounds? I'm honestly not sure how many tho. It was very dirty I know that. It ran 100% flawless. The gun is relatively new too. But I also do not know the round count through it. I would oil the bolt to receiver areas with basic CLP on almost every time I used it once it really looked dirty. I don't over oil tho. I use a needle oiler bottle so I can put it exactly where it needs to go.
I have never put factory ammo thru my MPX' so I cant speak for that. I've tried many different powders and have settled on using Alliant Sport Pistol. I do NOT use coated bullets as they foul up the gun and comp real quick. I've had amazing accuracy with RMR 115 FMJs. I can do a 1/2-3/4" group bench rested at 25 yards which is also my zero. I also use Everglades 115 heavy plated projos. But for my "major match" ammo its the RMR 115 FMJs. I prefer the quick recoil impulse of 115s. I've done 124s and 147s. I prefer 115s.... I do 4.5gr of sport pistol under a 115 @ 1.135" which makes right around 140pf. Its a gas gun, give it gas...
I do know the MPX is a lot of work to clean. The gas system isnt difficult but its time consuming. Some people just swap out parts and ultrasonic the ones they took out. I dont do that. If I were getting into PCC right now, I'd 100% look at a JP5 over a MPX. Having shot the JP5 multiples times now, I still prefer the recoil impulse of my MPX over others JP5s. That being said if I tuned the gun to shoot how I like, I'm sure the difference would be negligible