I don't think it matters. If he can reach 61mph he should have the revs to accelerate all the way up to 80+ mph in 6th gear.
The patience of the O.P. is unknown, so while I agree with your assessment (which does suggest that the clutch is going out), I'd like to be sure that it isn't newbie misconceptions before suggesting new clutch plates.
And if it is the clutch, he should hear the engine winding up and be able to see that with the tach. None of that was included in the description.
It could be something as simple as rodent debris in the airbox, or an oiled up air filter.
I agree with John, given the lack of information in the opening post, one could speculate and play the guessing game until the cows come home... without some specific details from R0gue4, I wouldn't waste time on this thread.
Bike's a 2011. Purchased used in 2013. Took about a year working my way up to venturing onto the interstate. Reaching 70mph and above in last gear wasn't an issue then. Now I kick up to last gear and can max out the throttle with no jump from the rpm needle and i can't get above about 61mph.