Today I test casted both the 590-4 and 690-4 Sage Z-Axis. I was surprised as to the amount of difference I felt while casting these two rods. The 6 wt, for lack of a better word, had a stiffer feel. Makes sense since it a heavier line rating. I mainly fish lakes, streams and rivers in the Sierras for trout using dry flies. What I would like to understand are the features (advantages) of a 6 wt that a 5 wt does not have.