I've been down before. Spent a week there a few years ago, but it was a family trip, so the trip wasn't fishing centric and most of my trips were rather short escapes, so I really couldn't get back in there away from roads as I'd have liked.
- a couple of short trips on Cosby Creek as we were camped there for a few days. Fished well, my favorite of the trip. Mostly bows, a few brookies, 1 brown.
- Little River upstream from Elkmont. Didn't fish great, and this was my larger trip and I spent a good portion of a day there. I did catch a couple of bows and 2 fairly nice browns (low teens).
- Roaring Fork, right along the motor trail thing out of Gatlinburg. Only fished it for like 45 minutes but it fished EXTREMELY well in terms of numbers. I got into double digits in that short time, and right by the road. All smallish bows.
- Middle Prong Little River - Near where the Thunderhead Prong and Lynn Camp Prong merge to form the middle Prong. Did ok. All rainbows. One that surpassed 10".
Overall, yes, in the park, pretty much every stream large enough to hold fish, which does not get too warm, does hold fish. Rainbows dominate the landscape, but there are places with brookies, and pretty much everywhere has a few browns. More browns in lower elevations as streams level out and begin to warm a little. A lot of the larger streams, as you get lower on them, do warm too much for trout, though smallies pick up the slack, and there is overlap, and they do stock trout outside the park. I'd also note that the streams have somewhat of a boom/bust flow. i.e. the lower end of your width range, 5 ft wide, may dry up at times and thus not hold fish. While I caught brookies on Cosby Creek, I was told the brookie centric streams are mostly the high elevation ones, which I did not get to.
Abrams Creek is probably the most famous stream on the TN side. It's a limestoner like chem and character and known for bigger fish and pickier fish. I didn't fish it but did hike along it from Cade's Cove down to some falls. It's fair sized along that hike, and looked inviting, but a totally different character than the other streams. More a gentle flow with small cuts and crevices, whereas the other streams were steep and wild freestoners.
Gatlinburg has a fly shop. I did not visit but it looks small and touristy, and everything in Gatlinburg was overly touristy and with too much traffic. I did not really like that town. I did like the Cosby Creek area, although it only accesses a small corner of the park and you can't get to the main park roads.
Townsend was a nice place, more laid back, and with direct park access. There is a large, very, very nice fly shop in Townsend, called Little River Outfitters. I was very impressed with their operation. They give a lot of info and have a well stocked shop. They also have an active message board and a website loaded with info.
http://littleriveroutfitters.com/
I'm not of much help on the NC side....
Castability wasn't difficult but the water crystal clear and the fish spooky, and generally a little larger than our small PA freestoners (the small ones, again, dry up at times). As such, you need a bit of distance on the casts. I'd recommend something in the 7-8 ft range, 4ish wt. Could easily get away with an 8'-8'6" 5 wt too, especially if you have eyes on the slightly bigger waters like Abrams and Little River. The fish aren't big, though.
