I am looking at these tires too.... I talked to the guys at Dixie 4WD in St. George cos I noticed they are a dealer and have a coupla sets on their JKU builds.... they are also running the 39x12.50R17 and they do look narrow but this increases contact pressure which increases traction. They confirmed that they are soft, sticky and not a hi mileage tire.... A key word here? Yep... Sticky. Music to my ears.
Now as far as the E load rating? my PBRR's in 37" flavor are E rated and flex great at 8-10 PSI but as mentioned above have a thick carcass and are tougher than the C or D tires I have tried in the past. I will only run a E rated tire if I can help it.. I also read that the new BFG KM3 will be E rated exclusively for this reason....
I am wanting the 39x13.50R20 however since I acquired a set of 20" TR's recently and prefer a the shorter sidewall for my kind of wheelin. Plus I have a theory on tire sizing specs that may happen on the pipe dream tire that may never exist. The 40" PBRR....

This 39x13.50R20 size is $280 per so I believe I will give them a shot as soon as I get my 20"s ready.
Hope to find more feedback on them in the mean time..... :stirpot: