at 80 mph it felt just like my old 89 Sportster 883 felt at 80 mph: vibrational, and not just not happy. 80 was pushing it. Even 75.
Sold that old 883, too for the same reason.
Since then, bikes I've had that
were happy at 75/80 mph - (even @90 in the case of the first 2) - are an 87 Honda Magna, a 02 Suz SV650 and my current 07 1200 Sportster.
Sure I could have given the XS a smaller back sprocket to bring the revs down, sure I could have re-phased it to try and make it smoother...but I just didn't feel like that was the answer.
If yours makes you happy all day, at those kinds of speeds, then that is great! I like your bike, btw. Is that a 79, too? (oops I just saw, your is a 79)
I like the XS engine best as an around town and smaller highways kind of bike. For riding in the city I actually prefer it to my 07 Sportster. But for long interstate rides... not so much, so at the time, I sold the 79 and got the SV650, which was a neat bike, but a little soul-less.