For what it is worth, my last 550 thumper was a 47 Ariel back in the 50's. The speed limit on OK then was 55 at night 65 in the daytime, and being young at the time, that is what I did and sometime a little more. One of my friends had a 48 Norton International and it was way faster than the Ariel. But to the point, my Electra has 1500 miles and was "RUN IN", that is the English term for break in, properly. Just like I run in my 48 MG after overhaul. I live 50 miles from Tulsa, 45 of which are 4 lane. My last 2 trips to Tulsa I ran at 61-62 indicated. That is where the thumper seems to smooth out. I see no reason why any late model 500cc single would be damaged at that speed. Oh yes I still need a taller windshield.
Don't you hate it when us old guys put in there 2 cent worth, HA HA