I am considering doing this to one of mine (Stainless Steel) but had a bad experience with the cerakote causing a very reliable firearm (MP5) to not work well after the coating.

(Full Disclosure - this was before bake on cerakote which may be thinner/better)

No, but I duracoated a W.German p226

ETA:  I didn't paint the rails or the internals (obviously) and it functions just fine after the painting

No, nor would I, but I love the SS finish on my L1.  

First, you would need to sandblast the entire gun to profile the surface, giving the Cerakote something to hold on to.  Then, depending on who does the application, you're going to be adding a few mils of material.  The X5 isn't known for having loose tolerances, so you COULD run in to cycling problems.  This could be avoided if you just did the exterior of the gun, but that might be fairly difficult to do well.  

In my experience, the X5 cycle feels like glass lubed with butter, and nothing I own with Cerakote on it feels anywhere near that smooth.

Thanks for the reply. That's what I was thinking too. I've decided it's not worth risking.

Good idea, my X-Fives are tightly fitted and I doubt they'd run right with Cerakoted rails.