Been there, done that.
About 7 years ago I bought an 1100rt.
As per yours, the clutch slipped when at around 5500 rpm in 5th gear, but not all the time.
Saw a new "ceramic" clutch plate one Ebay bought it for £95.00.
Installed with new heavy duty pressure plate from
motorworks.
Gearbox had to be stripped to every last component to replace clutch pushrod oil seal.
Verdict: "Ceramic" clutch is misnamed. It is a sintered bronze clutch using similar materials to that used in some tractor petal clutches.
It is grossly overpriced for what it is.
It is also superb, with identical charecteristics to original.
If you go down that road, do not install heavy duty pressure plate. It is too heavy for town use.
Myke