Ok, have done some testing this morning using my trusty Combro. For consistency I used RWS Hobby, 11.9gr. I did three sessions, first with a Webley QGS silencer fitted, second with a Swift Stumpy silencer and then with no silencer at all. Temperature indoors a pleasant 18 degrees.

With each of the silencers fitted I was getting a (disappointing) average of 5.5 ft/lb. Moving to chrono with no silencer, I used the standard practice of inserting a small square of paper between the muzzle and the Combro, which negates false readings from gas on CO2 guns. Oh my...output up to 8.5 ft/lb!

Just been chatting with my mate about this, and we reckon the RP5 system with choke does not like silencers, possibly due to the physics of what happens when the pellet emerges from the choke. I couldn’t see any clipping on the silencers and testing two seems to rule out a silencer problem.

I’d be very interested to see test results from Umarex with a silencer/moderator fitted!

So, in summary, the RP5 Carbine meets or exceeds its stated output...as long as you have not fitted a moderator!
Any views welcome!