Honestly, unless you're running two out of the following three (or all three):
Short barreled rifle
You're not really getting anything out of a piston AR outside of being able to say you have a piston AR. Keep any AR wet with oil, and it'll run and run assuming the build was within spec.
I do make a living selling these things, and will sell a customer whatever they want (DI or piston), but having shot thousands and thousands and thousands of rounds through AR's, both piston and DI, short barreled, full auto, etc., there's no real gain and depending upon the design of the system some problems that can drop up.
I also teach rifle marksmanship and compete in 3 gun, and I'm curious as to why you have to have a piston AR.