Lots of great points, Stan, especially this:
"If you have comfortable seats mounted low enough in the car to get you behind the windshield, you have an effective wind-deflector behind your head, and you have the side curtains (or windows) - you can drive all day and into the night."
I've got all of that, but at my slowly advancing age I'm pretty much all done after three hours. I think it's the drone, and maybe my newly fitted "Ear Peace" ear plugs will give me a little longer drive time. I can easily do a 3-4 hour jaunt around New England and my low-slung, Cabriolet-like seats stay comfortable - Way better than the 914 seats they replaced, so seat style, fit and position is critical.
My F250 had what looked like shallow, almost bench-style, saddle-leather bucket seats. They didn't look comfortable at all, from a "sports car" point of view, but we would put in 800 mile days on them two days in a row and felt good at the end of the day. Somebody thought out their design to make them comfortable.
Back to the Speedster, My revs, with a .89 fourth and a 3:88 rear, are usually under 3500 on a highway and I do as many highway miles as back roads. That gearing is great for Interstates, but I end up stroking between 2nd and 3rd a lot on back roads. Life is a compromise, isn't it? I just adapt and keep my foot in it. Getting up between 3750-4000 on a highway doesn't bother me, nor do I see it running appreciably hotter, but that could be due to my extra cooler and it's size and good air flow back there.
Whenever I'm out there on I-90/95 or others, I'm reminded of Norm Brust and his original '62 Cabriolet. Put him on a highway and he ALWAYS ran at around 80+ and close to 4K rpm and did that for well over 100K miles with nary a problem. These are tough little engines. They'll take it