Overheat is usually used to break walls. But considering your using it in sun Fire Blast will be hitting very hard also as well as allowing you to continue a sweep. So for that reason run Fire Blast. Though run Overheat without sun.
;) Sorry but I can't let you run that spread and nature.
252 atk / 4 satk / 252 speed and hasty :) I'm not letting you run serious.