I've seen elevated temps from clogged radiator fins, if its packed full of mud and grit it will cause catastrophic temps. Also if ur doing prolonged riding in high temps I'd consider engine ice or wetter water should help lower your temps some
I have a 4mm cub and I run with 10mils all day Long. A properly set up 4mm should, 4mm dm is pretty sweet make great power and its a 550cc 4mm pretty badass if u ask me