I have the self-produced heavy cap on the 4th of my Prestige 2052 as well as the lefreque plates which I find extremely performing. ( on my instrument). Curiously Steven Mead, during a masterclass I attended last fall, noting the additional weight on the 4th, he said that on the Prestige it was not good ( he didn't say the reason), while it was indicated for Sterling Virtuoso. In my humble opinion he was wrong.
2007 Besson Prestige 2052, 3D+ K&G mouthpiece; JP373 baritone, 4B modified K&G mouthpiece; Bach 42GO trombone, T4C K&G mouthpiece; 1973 Besson New Standard 3 compensated valves, 3D+ K&G modified mouthpiece; Wessex French C tuba, 3D+ K&G modified mouthpiece.