I have only used a 5wt on chum. At least partly because that is what I had. Worked fine on fish up to 10-15 # (scale weight) but the bigger ones didn't seem to know they were hooked.

This was fishing in smaller water like Kennedy Creek. In big water, like the Nisqually, Skagit, etc. the added streamflow and the ability of the fish to use it might overwhelm the rod.

As to flies, my best luck had been with green bodies with some mallard flank wings.