The biggest rule of any tippet selection is to make sure are using a similiar type of line as your leader. Try to match manufactures, re: if you are using Rio leaders use the same type of Rio Tippet. Copolymer to copolymer, copolymer to monofilament will decrease your knot strength by a good percentage. As far as tippet strength for winter runs #8-#12 test, summer runs can go down to #6. I am speaking from a North West perspective, you guys in the midwest I believe go all the way down to #4 test.