As for the 4 vs 6 arguement, remember that the car is a system. Different engines get different gearing too. Slushbox vs manual also matters in the feel. In a car for general car uses, it doesn't matter as much.
Now, if you're talking trucks and using the truck as a truck (with spark-ignited gasoline engines) displacement > Turbo. In light use (using the truck like you would a car) the turbo-downsize thing works but if you load it down with a trailer or heavy load, the engine no longer cruises at stoich off-boost, it's in boost and runs rich to mitigate cylinder temperatures and knock. It also pushes the engine from the peak efficiency (volumetric and thermal efficiency) toward peak power whereas most larger engines are set up to be in the less efficient but lower rpm range to cruise and towing puts them at peak torque (higher volumetric and thermal efficiency). Of course all of this is very general and varies on a case-by-case basis. If you go big enough non-turbo it'll never be efficient.
Not really necessary with newer engines, smaller filters, and thinner spec oils. Dry starts from oil changes are one of those things engines are tested to endure. On startup and idle, turbos only spin a few hundred rpm and the residual oil in the system is more than enough to prevent damage.
If you're that worried about it this'll really make your eye twitch: you're doing more damage unplugging the ignition. You're injecting fuel without igniting it so you get blowby diluting your new oil as well as dumping raw fuel down the exhaust. You should be disabling fuel injection, not ignition if you want to prevent problems.
Now, if you're talking trucks and using the truck as a truck (with spark-ignited gasoline engines) displacement > Turbo. In light use (using the truck like you would a car) the turbo-downsize thing works but if you load it down with a trailer or heavy load, the engine no longer cruises at stoich off-boost, it's in boost and runs rich to mitigate cylinder temperatures and knock. It also pushes the engine from the peak efficiency (volumetric and thermal efficiency) toward peak power whereas most larger engines are set up to be in the less efficient but lower rpm range to cruise and towing puts them at peak torque (higher volumetric and thermal efficiency). Of course all of this is very general and varies on a case-by-case basis. If you go big enough non-turbo it'll never be efficient.
But you are correct that after an oil change it is not a bad idea to try to spin the engine without firing to get the oil pressure up. On the other hand, there are some engines that have check valves in the oil system to maintain pressure so that at fire up you already have some oil pressure for early lube.
Not really necessary with newer engines, smaller filters, and thinner spec oils. Dry starts from oil changes are one of those things engines are tested to endure. On startup and idle, turbos only spin a few hundred rpm and the residual oil in the system is more than enough to prevent damage.
If you're that worried about it this'll really make your eye twitch: you're doing more damage unplugging the ignition. You're injecting fuel without igniting it so you get blowby diluting your new oil as well as dumping raw fuel down the exhaust. You should be disabling fuel injection, not ignition if you want to prevent problems.
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