The point was that wear is essentially the same, and plenty of late model stuff buzzes down the highway around 3K even with OD.

Of course the connecting rods and pistons will see more stress on a bigger engine, that's obvious.

I personally try to keep it to 3K or less as well.

I don't think I have ever worn out a muscle car engine. But I have managed to damage or destroy a good number. So wear wasn't at the top of my list of considerations.

Actually.............
1. If properly designed, the parts of a V8 DO NOT see more stress than those of a properly designed 4. Stress is defined as force / area. Sure the forces are higher, but so is the area. Mechanical things are designed either to a maximum stress or a factor of safety.

2. If the 4-cylinder is more than 2 liters, chances are it has a pretty long stroke. Strokes of 3.7 to 3.9 are not uncommon in the 2.4 - 2.5 liter range.

3. Running the "big V8" at 3500 rpm for hours isn't outside what the designers built into these engines. The same basic engines were used for industrial purposes and many ran at 3000 or 3600 rpm for their entire existence. Trucks also run at that speed, at least they used to. If your engine comes apart after 100 hours of 3500rpm speeds you did something wrong.

4. No, the engine's natural frequency is not the same as the redline. The redline is the maximum safe speed for the engine based on the design stresses. I don't believe there is an identifiable natural frequency for the complete engine. There are natural frequencies for crankshaft, camshaft, rods, pushrods and valvesprings. There is a natural frequency for cylinders, and as they aren't all the same configuration, every cylinder could have its own. But as an assembly it would be very hard to identify a natural frequency for the engine.

5. There are two problems with running high rpm: wear and noise. Running the engine more rpm per mph (gear ratio) increases wear on the moving parts in the engine. This cannot be ignored. It is up to the owner to decide how much to tolerate. Higher driveshaft rpm with lower gears mean the driveshaft is closer to its natural frequency and stresses the universal joints more.
The same is true of noise. Noise increases with rpm, and noise causes fatigue in the driver. It doesn't matter so much to the passengers, they can take a nap. But the driver needs to stay alert.

I changed from 3.91s to 3.23s in my '64Dog and surprisingly saw no difference in gas mileage. But, after a 600 mile trip I was not so worn out with the 3.23s. I did notice a considerable dropoff in acceleration ability around town, and so that part of driving became less fun. I also did not want to invest thousands in an overdrive, although that would have solved both problems.

R.

High rpms on a Mopar not a problem in my option. The main reason I run them is when I was young dad had a 66 Chrysler 361 cid, most driving at 100 mph plus, rpms at 3500 plus. We put 660,000 miles on this car over 20 years like this, oil and filter changers every 2,000, the only work on it the was a couple of timing chain and gear sets, and at 380,000 miles new rod bearings rings and oil pump, no re-bore or other parts, oil would be down 1/2 quart at oil change when car was parked, pulled engine and put in my 70 Coronet for another 35,000 miles still ran good when I parked that.
74 - 318 truck drove the same for 230.000 miles no problems there either till the timing chain chain broke and bent valves( at the track with engine near red line ready to shift from 2ed to drive ), could have fixer easy most likely but gave a good reason to install a 440 in the truck.