They eat them like popcorn, but why worry with something when anything which is close will work? The Holston fish are far from difficult to catch, tie on some sort of dark nymph and go with it, don't make things more complicated then they are on the surface. Despite what Hugh says, they always eat them, there isn't much else too eat in that river. There are no mayflies to speak of, and caddis make up 90% of their diet.
One battle which is tough is when they get keyed in on caddis emergers, rather then get bogged down with that fight, take 30 mins on the bank and let them switch to adults.
I just cannot for the life of me figure out why you would want to take something painfully simple and make it into a quantitative analysis problem.