Kind of related, we used to run F450/550 DRW diesels in our fleet. Moved to the F350 DRW platform, and ran them at Max GVW - same application as the F450/550. Saw our costs go down as the parts wore out at the same intervals, but F450/550 parts were more expensive to replace. Talking 100's of these trucks in our fleet.
A case of over-speccing not saving money, but costing more.