As Ben has already pointed out I fish a 10' rod from the tube and boat (a 4wt Helios) and have yet to suffer any issues at all in the 'tube. I see what Mike is probably suggesting, but if you're canny and have a suitable net with a decent handle length for using in the 'tube I don't see any reason not to buy a 10' rod myself.
That Helios is very much my 'go to' rod for really anything trout related other than streamer fishing and if I had to choose an all rounder for tube and boat then it would be 10' - no question.
I wouldn't dismiss the idea of a 9'6" rod, but given the choice it'd be the 10' every time. Although others may have a different view, I see rods of 9'6" and over as a positive advantage from a drifting boat. Equally, I can see the merits of a 9' rod for 'tubing - but 10' would be my personal preference.
As to line weight.... hmmmm. I can see advantages in having something in the 5 or 6wt territory, if only for (maybe) a sinking line and lure fishing for 'bows or perhaps chucking something a bit heavier about for Sea Trout or (even) the occasional Salmon making the rod more of an 'all rounder' for you. Then again, if you don't see yourself doing much of that then the Western3 #4wt that Ben uses is quite happy with 'proper' sized loch flies and having had a chuck or two with it I suspect it would probably cope with pretty much anything you cared to fish with. I quite like it and would consider one although if my recollection is sound it's a 3 piece. I have yet to try the Access so can't pass comment.
I'll be intrigued to try out this new Sage that Sandy has crafted (he builds a nice rod, by the way
) as I have yet to pick up a Sage of recent times that I haven't immediately got on with.
H