There is one big difference between cars built before the mid '50s and those afterwards: it wasn't until then that there were many places in the world with modern controlled access, high speed highways. The first modern highways were Germany's autobahns in the '30s, then a few freeways here in the US in the '40s. Outside of these most non-urban driving was done on indifferently surfaced two lane roads with frequent intersections, which kept practical speeds down in many areas to 50-60 mph.
Constant high speeds will overstress a poorly designed engine, most particularly in the bottom end. Some pre-'50s cars had plenty of bearing area and good oil supply, but some didn't. I'd feel comfortable running all day at 70-75 mph on an interstate in a well-maintained car from the late '50s on, but with a prewar car in particular I think it would be best to stay on secondary roads and keep the speeds down.
There is a famous story about some troubles Rolls-Royce had in the '30s when the autobahns first opened. By the standards of the day, most R-Rs were quite fast cars and of course very well built. Some wealthy Britons were used to taking motoring vacations to the Continent, and when they first discovered the newly opend autobahns they simply put their feet down and ran the cars at 80 mph plus. The result in some cases was overheating, in others bearings failed with catastrophic results. R-R had to admonish their customers that top speed and cruising speed were two very different things. This might seem pretty self-evident, but in Britain of that time there was simply no place outside a racetrack that one could maintain autobahn speeds for long enough to damage an R-R engine so it had never been a problem, though undoubtedly R-R knew of the limitations.
Here in the US the Chevy "stovebolt six" was a mostly laudable engine, smooth and reliable and with overhead valves, but until '53 they all had the very nasty combination of heavy cast iron pistons and splash lube for the rod bearings (no oil galleries to feed the rods). My father experienced a failure in his '53, one of the last splash-lube Chevys, on a long drive in '58 from LA to east Texas. He'd bought the car new and maintained it well, but somewhere in west Texas one of those rod bearings gave up. Being an engineer who grew up with Chevys, he was able to drop the sump and rotate the bearing around, then removed the spark plug wire so that cylinder wouldn't fire. He made it the final few hundred miles of his trip on five cylinders, then bought a nearly new '57 Ford as he knew the Chevy wasn't really up to interstate driving.