Hey guys, I'm no entemologist (I can't even spell it), but I would say that is a size 20 BWO. My buddy has a retractable hard cover over the bed of his pickup truck and there are always several mayflies on the cover when we get back to the truck.
As for the 8X, that was more of an experiment than anything. I usually use 6X, but have found that some days require 7X, just playing around with the 8X. The one fish that I had on and lost was a very good fish. I didn't break him, the hook just pulled out.
As far as hatches go, you can always expect midges (I hate 'em), look for some BWO's and if it is sunny you might see some sulfurs. I would hate to be on the South Holston without sulfurs any day of the year, just in case.
Monktrout, I will check into the whipped loop.