bypass oil filter
I think the bypass oil filter system is probably the best mod you can do on a 7.3 or 6.0 due to the oil hydraulic fuel injector system. Anything you can do to ensure a clean flow of oil to the injectors will be the best thing for them. As for oil change interval, there are lots of stories, look at the amsoil website. Those people who extend their drain interval use an oil analysis service to tell them how their oil is doing.
It is up to you to decide whether you want to use the bypass filter and normal oil change intervals, or extended ones with oil analysis. I use the bypass filter and synthetic oil with more normal oil change intervals. I do find it odd that there are people out there who will blow a wad on big tires, tuners, turbos, etc, but consider synthetic oil too expensive. These engines are very hard on oil, due to the hypop fuel system and egr system. You get dirty oil, and you got injection trouble. You get oil viscosity issues, you got injection trouble. Proper viscosity (5W40) in the winter, using a synthetic oil, and a bypass filter, gets you clean, stable oil that the doesn't give the injectors fits. In my humble opinion, the hypop system, egr, and turbo all give the oil hell. Synthetic handles low and high temperatures significantly better than dino. Synthetic will won't coke up your turbo bearings like dino will, will flow better at cold temps, and won't break down under high pressure and temperature like dino will.
Nothing will kill a 6.0 faster than dirty fuel/ oil filters, and dirty old oil.