I can hold 65 steady and comfortably. 70 is starting to feel like bike abuse, but it will hold it fine. Not tried it, but I'd expect it to be tiring holding 70 for long periods. The problem comes with overtaking, it needs a run at it. If you are happy to stick with the heavy traffic, with overtaking when there's space, it is fine on motorways and dual carriageways. A 19T sprocket is the way to go for regular higher speed routes. Apparently, it lowers revs enough to calm it down around 70, but won't improve overtaking.