Yeah, you're right, I think these forum sections have pretty much been taken over for editing discussion, but there's not exactly anything that specifies this, so...
I live in Knoxville and I did a similar trip last year, plus I've driven all of those routes. I opted for the 64>79>68 route then hit I-95 and the turnpike (and tolls!) from Baltimore. Other than the cost, I loved it. I-79 and I-68 are not only more scenic, but they have FAR less truck traffic than 81. (I should have turned north in Haggerstown to 81 and 78, but I wanted to mark off my map for completeness) The 71/70 route was just a bit too flat and dull for my taste but since I drove it at night I can't comment on the traffic.