Right now we again have a discussion on the Sexyloops fly casting board about fly rod efficiency. There have been several attemps to theoretically calculate the efficiency for different fly rods as they would offer it to us fly casters. But the simple truth still is:
I yet have to see a calculation, which takes the positioning of the fly into the target as the one reference. This is the only thing mattering in my fishing reality. In order to determine the efficiency of a fly cast one would have to check the fly path in detail. Instead just comparing energy input vs. output for the fly rod and only the fly rod does not nearly match my fly casting reality. A lot of additional factors (like loop shapes) come into play in my world of fly fishing.
Just one example:
When I see a fish rising and the rod helps me to put the fly within just one cast to the fish, this safes me a lot of (especially mental) energy. Oh, and who knows, I even may catch the fish. That easily can safe me energy for the whole rest of the day. ;)
Physicists like to differentiate between efficency and effectivness when it comes to fly rod comparison. I personally believe that one can't live without the other one. Let's imagine a fly rod allowing me to transfer a high percentage of the energy I put into it directly to the fly line. Such a rod would be very efficient as some physicists tried to explain me. That would be, even if my cast would fail to reach the target. Well, I believe a failed cast will always be a significant waste of energy (not efficient at all) and probably I would try to make a (new) better one then. Would that be efficient? No, of course not!
When you want to compare fly rods I mostly recommend to give those rods a go and check how your casting FEELS and LOOKS to you when trying to position your fly to your target. That (and I think only that) includes all important key factors in your fly fishing world. Yes, even those small ones we probably yet do not understand.
No surprise to me we have all kind of very different fly rods on the market. Each of them has it's fans based on matching best for their personal fishing situation. As long as you feel fine with your fly rod, I think it mostly will be pretty effective and efficient for you. Besides that we of course need serious experience in testing and comparing rods.
During the last days we have been teaching fly casting a lot. It's exactly here where I can see, that a fly rod does not just come with one level of efficiency. Efficiency highly depends on the driver and how he uses whatever fly rod to position his fly.
I hope you'll be happy with your next fly rod though! My number one advice: Before you buy it, TRY it!
All my best
Of course I was fishing inbetween the lessons. ;)