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If 10w30 works fine in a 15L engine pulling 80,000 lb in desert and mountain passes, not sure why it would not work fine for what you are doing.
But those engines are made and tested for the 10W-30. Griz has modified his engine. His mods put more stress on the pistons to main bearing parts when he's running hard. This is why I suggested a higher viscosity oil with higher film strength.
A 777 jet engine puts out 90,000 hp with 5 wt oil. A very large diesel engine puts out 100,000 hp with 30 wt. crankcase oil. Those do not relate to Griz's specific situation. The psi of the bearings is important. Not the psi of the oil supply, but the pounds of force of the piston pushing down on the square inches of bearing surface. The oil film must handle the force without failing. Griz has increased the force due to his engine mods. He can't increase the size of the bearings, so he might benefit from a stronger oil film. Other things remaining equal, higher viscosity oil has a higher film strength. The oil temperatures he shows aren't high enough to cause oil breakdown, but they thin the oil which causes a reduction of film strength. And, we don't know the actual temperature in each bearing--only an instrumented engine in the test lab has all that--but the bearing temps are higher than the sump temp.