I smallie fish from a kayak and use a 5 wt rod with 6 wt line. No problems but I am casting mostly size 6 flies. When the water levels went down I started wading more. And I used a 4 wt rod casting the same stuff for no real reason and had a lot of fun.

Now I am going out in the winter and getting ready for spring stream flows. That is mostly serious lead chucking. I am going to try a 7 wt and maybe a helmet. Most flies will be weighted and in the size 2 to 4 range.