Black or olive (or a black & olive!) bugger - size 10 or 8 fished on a 4X tippet. (I'm seeing a theme in this thread - long live the almighty woolly bugger!)
If you want to be potentially more effective, add a 10-12" dropper of 5X off the bend of the bugger, and add a smaller nymph, like a caddis pupae, a soft hackle wet, a zug bug - or get old school and fish a neat old attractor wet fly pattern like the Parmachene Belle, Red Ibis, Partidge & Orange, Royal Coachman, or Leadwing Coachman.