I have a 4" muffler, which has about 75% of the EGT reduction as the full 4" system. However, if I were to start a lot of heavy towing, I'd go with the full 4" exhaust.
I put a K&N Aircharger system on the truck when I first bought it, then replaced it with an Amsoil in the stock box, though I did open up the stock box a bit. This mod was entirely unnecessary, as dyno tests have shown there is no HP difference--at least up to the 150 HP Edge box, regardless of the intake system. They even tried it with no air filter at all. I am now back to a stock intake.
Tests run by Testand Corp showed the K&N flowed around one percent more than a AC Delco paper air filter when both were clean, but the K&N, Amsoil, Uni, etc all hit 10" of restriction in 20-30 minutes while it took the factory paper filter over an hour to reach 10" of restriction. This was a controlled test performed on a $285,000 machine. the factory paper filtered better as well. The advnatages of paper are widely known among heavy diesel equipment operators who run their equipment in harsh, dusty conditions.
I still have a K&N air filter, an Amsoil air filter, and a Uni Airfilter put away in a box somewhere...............
Anyway, like you mentioned, the key is in driving accordingly. I think the guys racing know what they are doing and should know the consequences. However, for those who have daily driver trucks and do things like set their chip on 120 HP and tow hard with no thought to EGT, well, perhaps they should do more research first.
All this reminds me of giys just starting in drag racing, who would willingly spend money to add HP, but were reluctant to spend money to build in durability and reliablility. I remember one guy who was pushing 700 HP out of his big block, but was unwilling to spend $300 for a spool and $400 for axles. I can't tell you how many times he shelled out his welded spider gears............
