Q. I am thinking about getting a 6-weight rod for light saltwater use. Has anyone used one? If so, what size flies can the rod handle? Is it a viable option for smaller fish?
There are rare places where a 6-weight (and even much lighter) rod can be used in saltwater fly fishing, but you have to choose wisely. The greatest disservice we can do the fish is to hook it on tackle so light that you exhaust the fish to the point of death after release. We should always fight fish on tackle that gives the fish a sporting chance and the angler the ability to land it in a reasonable amount of time.
Some examples of fish that a 6-weight rod would do well on are ladyfish, very small tarpon, small striped bass of less than 3 pounds, small jacks and snook under lighted dock, etc. In general, I would say if the fish weighs more than 4 pounds, go to a heavier rod.
I do not think an angler is a great fisherman if he catches big bonefish, medium-sized tarpon or any other large saltwater fish on such tackle. In my view, it is not only impractical, but also an ego-stroking tactic that any serious sportsman concerned about the fish would not participate in.