If you go up 26 the 421 route and the 58 route take the same amount to time. I like the 58 route because of the relatively mild hills to pull. The only drawback is the road is horrible when you crest the mountain from Virginia into Kentucky at Trash Hill.
From Winston DO NOT go any other way than 52/77/81! I have tried many different ways to get from Greensboro to Harlan and no way is as good as 77/81 IMO. 52N to I77N to I81S. Take exit 57A north on I26/Hwy23, stay on Hwy23 to Duffield, in Duffield at Hardees turn left at the light on 58/421, stay on 421 through Harlan, take a right on Hwy 38 at the Waffle House. From our area this route has the best roads and least grade. The pull up Fancy Gap on I77 and out of Duffield on 421N are the only major climbs. Takes me 5 hours from Greensboro with 1 gas stop and 1 rest stop.
For clarity I dont think there is anything to agree/disagree about. It depends on where you leave from. From WS/gboro 77/81 makes sense. For anyone Charlotte or south or west 26/58 is much shorter. From Charlotte I can be in evarts towing in 4 hours and 20 minutes. Its 6 plus hours up 77.
From Fayetteville area we take 421 to Greensboro then do to 52/77/81/26/421 thing like stated above. Definitely stay on 81 til you get to 26 in kingsport then take 26/23 north til you hit 421. The section of 421 from bristol to gate city was two hours of pure hell with a trailer.
Like was stated earlier there's only 3 grades to worry about on that route and I don't think they're as bad as black mountain in my opinion.
We made it!!! The one pull on 421 that goes on for ever was kinda ruff, the excurin would not kick down.... I finally realized the floor mat was under the pedal and I could not go full throttle. (Yes there has already been short jokes made that I could not reach the pedals...