TRUE, I HAVE NEVER TRIED LARGE FLIES BEYOND SIZE 4 HERE. MAYBE A 1/0 OR HIGHER SPARSELY DRESSED WET WOULD WORK HERE IF THE WATER IS COLORED. I do not SEE IT WORKING WITH GREAT SUCCESS IN OUR NORMAL CLEAR SPRING CREEK TYPE CONDITIONS IN MICHIGAN WATERS. Of the above factors I think water temp is the biggest factor and conventional wisdom is #2, although I really do not know for sure.