I agree with what @Nocktavius is saying. What I don't agree is with people recommending 9ft 5wts.
If @Spookintrout stated that 85% of trout were caught within 25ft. what would be the point of having the shorter stouter rod?
As I stated before the trade-off for nymphing is MASSIVELY in the favor of the longer rod in terms of line manipulation (the added length 10+ ft. and above helps a bunch with line control), sensitivity and tippet protection, though I think tippet tippet protection is also factored by angling skill. It would be a good idea to purchase a rod that could tight-line effectively incase the OP wishes to explore that option down the road. Tight-lining with a 9ft 5wt is doable but not very feasible and the experience would not be very pleasant.
When discussing rods I much more prefer to compare specific models as the actions and tapers vary with manufacturers and rod models. If we simply look at the line wt of a fly rod and determine that a larger wt fly rod can inherently outperform a rod of a lower wt class than my 9ft. 6wt H3F should be able to out cast a heavy nymph rig better than my Hardy 10'2" 2wt... but it doesn't, and the is because the Hardy has deeper power reserves and is able to tap into those to assist in leveraging the heavier rig.
Let's discuss indicator nymphing in of itself, which covers a wide variety of fly weights and indicator sizes. I don't know what kind of nymphing the OP is looking to do but it sounds like he just wants to do standard trout indicator fishing, which doesn't necessarily mean huge indicators. Most of my lighter nymphing can be accomplished with a lighter football style indicator. Now if I get into the heavy nymph rigs where I am tossing a heavier half inch style circle indicator, yeah, I'd bump up to a heavier wt rod, and that probably would be the proverbial 9ft 5wt. I think indicator nymphers need to focus more on the indicators they use. A good balance between buoyancy and density. I like the denser Oros and Lightning Strike Twist on style indicators as they are less wind-resistant due to their density and float well, though not as well as an indicator made of lighter material. The point I am trying to make is that sometimes you have to tweak indicators to better suite the capability of a fly rod. In instances where I am fishing larger indicators I am not worried about indicator slap because the water conditions are turbid and the fish aren't going to be wary about surface disturbances. And yes, I also understand certain instances require super light indicators such as Ghostech or NZ style.
Lastly, I would like to talk about fly rod actions. I won't ever say that a graphite rod mimics an action close to how bamboo rod feels, but a the deeper flexing nymph rods present a closer flex profile, so the OP should in theory be more used to the deeper flexing nymph rods as opposed to the shorter faster action graphite rods. Getting used to to a longer rod takes some time too.