I was thinking about this topic over the past few days, because I decided to drive the Pagoda to our vacation home in France (a 400 mile trek Amsterdam-Antwerp-Brussels-Luxembourg-Metz-Nancy-Langres on main highways, with the last 30 miles on local winding roads) and back for an extended weekend stay. I decided to go with the traffic, try out the new Vredestein tires, and check performance and mileage in general.
I returned yesterday which took a bit over 6 hours, so I averaged about 70 MPH. The weather was rough yesterday, and in the Belgian Ardennes there was some heavy snowfall and one resultant bad accident, that had just happened a minute or so before I passed by it (car upside down beside the road, several more dented).
It's probably rare to see a 40-year old car keeping up with, and oftentimes passing, modern cars over hundreds of miles. I found the most comfortable speed to be between 70 and 80 MPH.
Over the weekend, I drove about doing errands maybe 100 miles. So, in short, plenty of opportunity to be spotted and reported here! Over the entire trip, I only saw maybe three other old cars; one, a Jaguar E-type from the late sixties looking pristine, in Vesoul - a city where cars like that would be extra rare. He had a local tag (French department no. 70) and we gave each other thumbs up.