I've been surprised with the QHY9 how quickly the 8" (F5) Newt saturates it. I know its known for smallish well depth, but didn't expect 5 mins would be an issue. Mind you I'm still very much in the learning stages - I've got the gain set pretty low though.
All this time I've been fighting to get my guiding good enough to go over 5mins, and now I find it might be safer to stay short.