Here are a couple reasons that to me, really give justice to stepping into a longer single hand fly rod.
Keep in mind I am talking about trout fishing here in Southwest Montana on our beautiful trout streams (rivers, lakes, brooks, creeks, ect.)
1.) Maybe the single most important part about nymphing for trout on the bigger water ways here out west, (or wherever you are in the world.) is the mend. This is very important and there are several reasons for that. It slows down the fly to the natrual speed of the current it is drifting in. Presentation is everything out here.. Secondly, it is putting a little bit of slack between the fly and the indicator. (If you choose to use indicators....) which you should, cause they work fine. So dont worry about the stink eye that the dude with the 8'6" 5wt throwing dries even in the 20mph upstream wind gives you. Its not a crime to nymph with a bobber. Just saying. But mending is going to put the fly in the zone all things considered. Putting that little bit of temporary slack between your fly and the indicator is going to allow the fly to sink and get into the water column that the fish feed in. So to get back to the length of the rod, 10 footers will give you a longer tool to mend with. The more line you can mend while working as effeciently as possible without repostitioning the fly, the better. I know its a lot, but just think about that.
2.) Water hauling/Roll Casting. A super useful cast for us nymph fishermen. When trying to accomplish a long drift, fishing big double fly setups, when casting in the wind, water hauling may be the single most affective cast, (for me) when throwing bobbers. The 10 foot rod is going to allow you to haul a little more line and also be a little bit more accurate with the placement of the fly upriver and out into the seam. Getting a long drift is extremely affective. The longer your fly is in the run the more likely it is to be eaten by a big trout. Roll casting is also something that will come in hand each and everyday if you are walk wading around our western rivers. Having a longer lever to work with will help you roll cast more line when you need to reach the lie out in the middle of the river, behind the boulder. (or whatever)
1.) Reach casting while presenting dry flies to positioned trout feeding in a lane is a game changer. The guys and gals up on the MO in the Craig area made that clear to us over the past few years in the recent films and videos from the region. Reach casting allows you to put a controled amount of "slack" if you will, in your line to allow the fly to float over the fish without moving. Like Mark, R. from Craig says, "Dead bugs don't swim." And thats just the reasoning behind perfecting that casting style. So get this.. Having a 10 foot rod is going to allow you to really exaggerate the basic principle of the "Reach Cast." Allowing you to pull back just a little bit more line, a little bit more effortlessly and in my unprofessional opinion, a little more accurately.
This one is not necessarily a good thing.. Its just extra. Just for your own entertainment.. For a little something different if you're into that kind of thing...
2.) Long Hook Sets.. Now before you start in, I know it is not what you want to be doing. Not what you want to be teaching new fly fishermen. Not what the doctor ordered.. You don't want to fish too far away because as we all know, coming tight on those fish out there at 40 feet is pretty damn tough.. And seems like its always a big fish that eats it way over there! Wouldn't reccomend even putting yourself in that position because your chances are slim at landing that fish.. BUT!!. But, if you are like me, and fish out there every now and again just for fun, get this... Fishing to those risers at 35 feet.. 45 feet.. sometimes 50 feet can be just silly. But with a 10 foot rod, you can haul enough line to present the fly nicely. Enough rod to pull off a reach cast that is going to have enough line on the water to keep the fly still as if drifts over the nose of that trout. And... and enough rod to pick up all that line quick enough and have enough backbone to come tight in time on that fish at that distance. It is a great way to hook fish out there under those circumstances. Granted you dont need to even cast at those fish when you can simply take a couple steps closer. But like I said, in those occasional situations a few extra steps isn't an option, or you just like to double haul.. Then it makes sense to throw it at that fish anyways.. Just cause you can..
Hopefully you took a little bit out of this. Hope it helps you in your quest to purchase a new fly rod for summer time dry fly fishing or for your new winter nymphing trips. And I hope you don't think that I dispise guys that fish 8'6" 5wts.. I think they are sweet. I was just making an example... Opinions over here... Save the hate mail.