It is my opinion that action does make a difference. The power of the rod will determine the weight of the line used. The action will determine how long it takes to load the rod completely on the back cast, and the speed at which the line is sent forward. This will affect the loop size, and require adjustments in casting technique. Weight forward lines will take longer on the back cast to start loading the rod, and so a faster rod (more stiff) will help store the line's energy in the rod faster, and deliver that energy back into the line faster on the forward cast. It ill give you more distance, and since there is more mass, will slice through the wind better.

On the other hand, a less aggressive weight forward taper will give you more accuracy, and better mending, and roll casting. It will also lay down more gently on the water, which may be important if you are targeting spooky fish. The top of the line will also land more softly on the water. I'm not sure, but I think that if the line weight is more evenly distributed on the part of the line touching the water, that line will pre-l;oad the rod better on the back cast, and so be more forgiving. However, after the line is off of the water, you still need ti use proper technique to avoid wind knots, or snapping your fly off when it is snapped forward too early, or allowed to touch the ground.

Oh, I'm beginning to ramble I'm shutting up now. Hope some of what I posted is useful.

Tight Lines, and Frisky Fish

RJF

A line with a long, decreasing forward taper should turn over faster than a weight forward line. As the diameter and weight of the moving line decreases so does its mass and the energy is converted to speed so the line "turns over" faster. Beginning fly casters invariably "whip" the rod back and forth before their loops straighten out. A long, decreasing diameter forward taper may be easier for them to time?

I put a RIO In Touch Technical Trout 6WF line on my Eternity2 9ft. 6wt. It is my first experience with a minimal stretch line. I only cast the line on the grass at a nearby park. It turns over quite well and lands with delicacy, which I desire. I was casting a 9ft 5x leader with about 24" of tippet. I can cast 55 feet with no problem (withouth double haul). The line feels just a tad light, but that is OK. I may get another 6WF like a SA Trout or Rio Gold if I desire more power for larger flies and nymphs. I think I can feel the difference in the no stretch line vs standard when picking up the line and in the way the rod loads. Line was on sale for $69, so you can't beat that.