I have the 300mm RPP. We used it on a number of shots on our feature and it was sweet. We added my doubler to get some 600mm action, which was even sweeter. Can't comment on the other glass but I can tell you we loved the results from the 300.
what kind of doubler are you using with your Red 300mm lens?
Scarlet-X #1103 "O'Hara"
Red One MX # 10086 "Retro"