Depends on your oil pressure, but I would run rotella t6 in the heat which is 15w40. Once the oil gets hot its pretty much same viscosity anyways. You cam run a heavier oil if your oil pressure is getting too low, but I doubt it’s going below 2bar at idle.
I added an oil cooler fan to my oil cooler to keep oil temps down. Worked like a champ. I don’t recall how hot it is near the red, but it’s nice to stay under 245f oil temps. Hotter than that is tuff on bearings. But I run like 300f oil temps in my race car all the time... however the engines don’t last too long at that. Haha