Foambug,

You can go down to an 18 if you are careful. However, dont' discount the effectiveness of larger size flies, even in waters where others typically use the 18-22s. Trout will take larger offerings when they can get them. Even on very technical waters you'd be surprised at how many fish, and usually the larger fish, will come to size 6-8 wooly buggers or leeches. Wet flies in the 8-10 sizes suggest several larger insects that the trout will eat, even in waters filled with midges.

Up to you, but I like that larger hook and the thicker tippets involved with them. I hook well and land more fish. Don't struggle with tying them on, and getting them out of the fish is easier too.

Buddy