If we ask a broad spectrum of the fly fishing community including fly casting experts, line manufacturers, and rod makers about the wisdom of underlining or over-lining our rods, the answer we will most likely get is that it's best to put the appropriate weight line on the appropriate weight rod.
In other words, a five weight rod should receive a five weight line. However, these days, we see even the line manufacturers challenging that concept. Line manufacturers like Scientific Anglers have created a line of fly line that is not exactly what it says it is. SA has a series that is slightly more than the box tells us - it's labeled a five weight, for example, but, is actually a 5.5 weight. To me, and I have been wrong more often than not, that's over-lining.
This past weekend on Blue River an over-lined rod went with me. I could not have been more pleased with the performance of this rod and line. And, the fish didn't seem to mind either.
The rod in question was one of the two Cabela's Three Fork rods that Charlie recently gifted me. No doubt, they are a little bit on the stiff side and rather fast. By over-lining, the rod was slowed just a bit, causing a bit more flex and the delivery was really nice.
Charlie was the one that suggested I over-line these rods and that's because Charlie has had a long history of rods, weighing fly lines for grains and all that whoopy-do stuff. Charlie knows what he is talking about.
There are guys out there that do nothing but cast fly rods and they are indeed good at it. That kind of thing doesn't interest me at all however. Just can't see myself in some competition casting on a landlocked area or in some casting pool where there are no fish.
The argument, or intellectual discussion, I should say, will go on and on for years. Some will say it's perfectly fine to over-line while others will rant as why it should never be done.
For me, it's quite simple. The fish could care less if we over-line, use the appropriate weight, or even if we under-line. It's not like they're down there in the water column and suddenly say, "Hey guys, get a load of this! This joker has a 9 ft. 4 weight and he's got 5 weight line on it!"
No, that conversation in the trout community will never take place. All the trout will be interested in is that natural drifting pheasant tail nymph floating my their head.
There is more to fly fishing than capturing fish - much more. However, if most of us are honest about it, we do like battling the fish the most.
Resting my case.