Agree on use of a smaller circle. Regardless of choke or distance I've never seen more than 22" of effective pattern diameter using any 3" shell in #7.5 or larger. Actual effective pattern diameter also depends on species. Always used coffee can (the old metal ones!) diam circles for phez, soda cans for grouse, dixie cups for WC. I think a 20" paper would do it. As stated, effective pattern is far more important than pattern percentage/nominal choke.
Also agree 25 yds makes most sense for 2.5" or 3", in the field shot sizes. Best quality 2.5" target loads in #9 and #8.5 can make use of 30 yds through some constrictions.
