The gray areas of vehicle use make it hard to know what to do. One gray area would be a 6.5TD family rig that tows only occasionally, but is used as a people mover most of the time. I'd probably lean more toward a fuel economy build for that vehicle - small port precups & factory CR. Plus I'd add a few other items that improve efficiency - like gear drive timing set, intake/exhaust mods, etc.

On the other hand, if the vehicle will be used to tow heavy more than occasionally, I'd build in some durability and power - like 18:1s and hi-cap cooling, along with turbo & fueling mods.

A little trivia.... The Duramax began with 18:1 CR in 2001, and now is at 16.8:1 CR.

Jim