I would say that the most common line weight people use for normal trout fishing is #5 and heavier. I do not get this. From very early age, say 12-13, I’ve mostly fished with 3-weights, almost regardless of fishing situation, in particular in streams and rivers. Only for sea trout and lakes, fishing with intermediate lines, larger flies and in windier conditions, I have sometimes, reluctantly, used a #5 rod. My number one rod has, for almost 20 years, been the #3 Winston LT5. I have actually owned two of them, both of which I built myself, as the first one was stolen during an over nigh train ride about 15 years ago. I got the money back from the insurance and had the chance to by any new rod that I wanted. There was no hesitation.
Since then I have owned many fly rods. However, most of them have been bought on sale to complement my Winston for those few occasions I did need to cast heavier flies into the wind. Naturally all these were compromises and so recently I thought I would buy the ultimate rod that would replace all of them. I figured it would have to be a heavier line rod. I was wrong. I have recently had the chance to cast quite a few rods, including SAGE ONE and Method, in different line weights. What strikes me is that I do not cast longer with a #5 rod than I do with the #3 SAGE ONE which I in the end went for. With this I can cast up to 30 meters, and it can easily handle my biggest flies I regularly fish with, which is typically a size 10 mini streamer with a 3 mm tungsten bead. What more could I ask for? What need would I have for a # 5 rod if I normally fish with flies in sizes 14-20 and up to 5x tippets, and still can comfortably fish at distances around 25 m. Even with a heavier fish on, I couldn’t play them harder because of the tippet. On the contrary, as some argue, you can actually land fish quicker with a light rod as it will allow you to put more pressure on the fish without breaking the leader (http://www.byrdultrafly.com/rodtip.htm). Thus, at the end of the day, for me it is the tippet diameter and fly size that dictates what line weight and type of rod I choose, not the size of the fish I’m expecting to catch.
Here’s one question for you: would you rather have a light line fast action rod (say #3) or a medium action heavier line rod (#5) for fishing with light tippets and small flies? I would probably go with the light line fast action rod (in lighter weights they tend to feel softer anyway). With this one I can get my fly out faster, while still being able to protect my tippet similarly to the medium action rod and at the same time use a lighter line which will scare fish less! Also, if you only have a fast action rod and need a bit more control and feel at short distances you can always use a heavier line. Of course, you risk spooking fish marginally easier, but now you really have two rods in one: a fast action #3 for long distances and a slower action #4 for short distances. Consequently, as much as it hurts me given my history with the Winston, if I only could choose one of my rods to fish with at all times, it would have to be the SAGE ONE. It is very practical and covers pretty much all my fishing situations, some of which, lets face it, the Winston would be useless for, for instance short line nymphing with heavy flies. I would, however, regret this every time I fish small dry flies at short distances, which is where the Winston truly excels. If I would get a rod to replace both of these I can think of only one: the #3 Winston BIIIx. This could be the ultimate all-round rod for me, on paper at least as I still haven’t had the chance to try it.