6.0 Powerstroke EGT Exhaust help?

Would like to lower my EGTs. around 800 degrees unloaded at 60 mph and 950 degrees unloaded at 80 mph on a level surface. i think these are too high. truck is stock just had head gaskets replaced and studded. I am going with a turbo back system to help drop the EGTs. is there a difference between 4 or 5 inches when it comes to this or does it not matter? i understand there is a sound difference and a back pressure difference but my biggest concern is the temperature. I know 5 inch can be a pain to get on and can only have a 4 inch down pipe max, but does it help drop EGTs more than a 4 inch system, even if its only minimal?  Thank you