The Pawnee Pass (12,541') - Buchanan Pass (11,837') Loop is a terrific, tough and super scenic 26-mile route in Colorado's Indian Peaks Wilderness. Here is a nice trip report on the route from Charles Danforth (from which I took the map and photo). More photos are here.
Note that times should be reported for a closed loop including the short paved section. Note included in the FKT list here is Bret Wilson's 5h45m in the 1990s, as reported by Bill Briggs. Note that this would have been the FKT until rather recently.
This route is very popular with Front Range runners, and there is a Strava segment which includes some quick times that aren't listed below.
Route map from Charles Danforth
Photo by Charles Danforth
Heading out this am on an unsupported long run attempt at the Pawnee Buchanan Loop FKT. Excited for the views!