Among the other bikes I've owned, my R5 was one of the favorites.
There were only a couple of things that turned out to be crucial, the first being don't try to make it do something it does not want to do. Mine would shake its head one time and lay right down on my left knee. Happily, they are not heavy beasties, and pick up relatively easily, although I should tell you that it's been more than 30 years since I had to pick it up.
If it smokes too much, odds are the oil mix pump needs adjusting - but don''t adjust it yourself to a no-smoke point - that could be followed shortly by a no-run point, and a large bill. It should smoke just a little at hard throttle.
They are good runners, although you're right in that they seem to hate a stead speed - but after all, it is a small Yamaha, and they're custom made for canyon racing, or for running up into Bucks County on some of the older roads. I'm a Hatboro class of 1960 graduate, so I know Street Road fairly well - you'd've been happier on a two-lane that was interesting - the four-lanes are best run with something larger and less intense.
The R5, when everything is just right, will run like stink, and embarrass many a larger bike, both at a light and back through the boonies. Mine spent a lot of time in the New Hope area, which was loaded with good practice roads.
Enjoy it - it is a fine machine, and should serve you well for years with minimal upkeep - just read the manual and do what it says.
And 79cb750f aptly adds:
Since it is the predecessor to the RD-350, the quintessential hooligan bike, you can do darn near anything to it racy.