Ray:
From fishing in Vermont on and off over the last 20 or so years, summer only.
I've seen Yellow Sallies and Lime Sallies
in the air along with some large brown or black stoneflies(adults were about 2 inches long)and found some large yellow/golden stonefly nymphs(an inch or so long) turning over rocks.

Not much of a nymph fisherman, so I won't suggest anything.
For dries
Yellow and Lime Sallies
Size 14 or 16 TMC 101
Body: appropriate color CDC feather wrapped on shank.
Wing: A white artificial hair
Hackle: Grizzly wrapped just behind the eye and trimmed flat on the bottm.
For the large Stoneflies
I just supersized a CDC and Elk on to a 4 to 6 2 or 3XL
Body: CDC feathers of appropriate color wrapped on shank
Wing: Deer hair