Rpm and something called bearing speed. This tears up oil.
Not crank speed but bearing speed. As the journal size increases, bearing speed does. In other words, imagine a 2.5 main turning 5000 rpm. Then, a 3 inch journal turning 5000 rpm’s. The bearing length increases for the same rpm. Lots more heat generated.
I have an engine with a 3.25 main. I can turn this thing to 6400 rpm. I run 10w30 most of the time. If I race it, it gets 20w50. If I run 10w30, especially in the summer, while racing, you will roast the bearings as the oil thins too much and allows the crank and bearings to touch.
All this gets worse as rpm’s go up. No matter the journal size. BUT, the larger the journal, the more intense conditions the oil has to face.
So, rpm’s, bearing speed, and heat. This includes towing on hot days.
Now one can see a 6.2 liter engine running on 87 octane, towing, in the summer, with 0w20 oil. Add long oci to the mix.
Not discounting the crank roughness. You will sheer the piss out of the oil. Spun bearings are in your future.