I'm sure its been talked about in the past, but I can't find it. I have Good Year tires on my p/u with only 30k miles and lots of tread left, but they are original tires. The sidewalls are clean no ...
If the truck gets regular use, I might lean toward the upper end of the range. A little bit of flexing while driving tends to redistribute the plasticizers in the rubber negating some of the UV degradation. If the truck is only used 3-4 times a year during trips, I would lean more toward the lower end.
A good option is as you hit 5yr start looking for tire sales. If you get them for 20% off, losing a year or so of use on the old tires isn't much of a hit.