I have a St. Croix, Imperial that is rated as a 5 Wt. and it simply didn't feel "alive" with a 5 wt. line. I put my reel with a 6 wt. line on that rod and did it ever come to life. I asked a similar question to yours on another board and received responses similar to what you have received. General consensus seems to be try a heavier or lighter line. The rod will tell you what it likes. Ain't gonna hurt nuthin'.

Vic