UPG may have been but what is currently?
The hardest trail I have seen lately was running Brittany Spear Backwards. The upper loop with boulders the size of full size trucks will be a challenge for any rig. But it is only 600 yards total.
The Hell's Trails looked hard (since I only made it through 3/4 of the first / easier one and walked the rest). The upper section on Chainsaw looked pretty hard (Kiel can speak to that more than I can).
The left side exit on Skull Canyon is the hardest, most technical section I have completed unassisted. Nobody else even got close
my claim to fame.
Upper Manera Wash caused me some serious problems. But if you are full width you can walk most of it.
It all depends on your setup I guess. Since I am 100 wb Long and narrow, vertical climbs make me pucker. Tight twisty technical trails are easier.
I am going to reserve judgment until I can run Price and Finish Hell's and Chainsaw this spring.