Re: Fly rod line rating, power, and action - an explanation.
Here is an additional 2 cents added to Silver Cr.'s excelent posting on rod load dynamics: A properly desiganted #5 line rod (of faster action) when overlined to compensate for a specific angler's slower stroke preference, diminishes the tracking and accuaracy of the rod by overlaoding the tip. Perhaps not on a short, lower line-speed cast but as greater acceleration of the line is called upon for more distance the effective "tip" is actually lowered into the upper section by the increased mass/velocity of the airealized line. Essentialy the tip is collapsing under load, increasing wobbling fibrilation in the tip section inducing bumps in the loop formation and decreased communication with the line.
There is, in my view, a common missconception that fuller flexing rods produce more delicate dry fly presentations than faster tapered rods of the same length and line weight. The sense is that the more deliberate timing feels gentler than the quicker, tight-loop geneating faster rod. Lets take a look at this: The slower rod, gentler stroke produces a more open, lower line-speed loop that delcatly unfurles upon the water delivering, with diminishing energy, a not fully straigtened curvey leader to get some extra drift out of the dry fly. It is also sending line impact, as it lands on the water, shook waves to the fish before the fly actually drops onto the surface as the line hit the water first. Conversly, the properly loaded quicker rod generates a higher line-speed, tighter loop that can be directed with improved accuracy, has the power to turn the leader over in mid air allowing extra time to execute a reach cast, in-air mend and, perhaps, give a little wiggle to the rod tip to generate the desired amplitude of curves in the line/leader assembly and directing the unfurled fly to the feeding lane as the line decends to the water's surface in a controled, precise manor.
Therefore, even on the smooth but complex, braided currents of a spring creek like Silver Creek, where the ultimate in accuarcy and delicacy of presentation is a perequisit for success, a faster (not stiff but well designed steeper tapered) rod, fished with the appropriate degree of casting acceleration will (in the hands of a capable angler) be the superior fishing instrument to a mid flexing rod requiring a slowly timed stroke. And, to stir your imagination further, a #4 or 5 rod will present a dry fly more delicatly than a #1 or 2 weight because the greater line mass permits superior in-air line control for precisly controled fly placement.