I'll start by saying I've never fished those streams, but I have fished similarly sized smallmouth streams not far away. This time of year, I'd look for the deepest water you can find. My guess is they will still be in the wintering holes and the deeper water right now until the water warms up. I'd say your fly choices are pretty good, you'll just have to get them down to the fish's level and slow them down for what will likel be less active fish right now. As for the 8' 4wt, I think that's actually a pretty good setup for smaller stream smallmouth. I actually go a lot smaller/lighter than that and have very few issues or even breakoffs.

 

I fished most of the summer on the fly and learneda lot. The fly choices I like a lot for the summer. Your post inspired my to leave my spin rod at home tomorrow. I agree with cream they are wintering now. I am going to use a sinking leader and buggers. I have been fishing in north Georgia for the last month for trout while working in the area, I debated the ten hour drive today if I should just fly fish on my only fishing opportunity on my weekend home. Thanks for the post man.

 

I have fly fished little darby up buy west jefferson-lots of overhead trees so a 8 foot rod is good-the stream is beautiful and very wade-able up there. I have had success fishing clouser minnows-generally keeping everything fly wise on the smaller side.
Guy I used to fish with would kill it with in line rooster tails on a a zebco reel.
I have not fly fished big darby but think your gear would be fine-the stream is not as wadable-deeper-so I usually take my canoe and spin fish from it or get out and fly fish.
If I was on darby right know I would probably spin fish deeper holes.

 

I'll start by saying I've never fished those streams, but I have fished similarly sized smallmouth streams not far away. This time of year, I'd look for the deepest water you can find. My guess is they will still be in the wintering holes and the deeper water right now until the water warms up. I'd say your fly choices are pretty good, you'll just have to get them down to the fish's level and slow them down for what will likel be less active fish right now. As for the 8' 4wt, I think that's actually a pretty good setup for smaller stream smallmouth. I actually go a lot smaller/lighter than that and have very few issues or even breakoffs.

I have fly fished little darby up buy west jefferson-lots of overhead trees so a 8 foot rod is good-the stream is beautiful and very wade-able up there. I have had success fishing clouser minnows-generally keeping everything fly wise on the smaller side.
Guy I used to fish with would kill it with in line rooster tails on a a zebco reel.
I have not fly fished big darby but think your gear would be fine-the stream is not as wadable-deeper-so I usually take my canoe and spin fish from it or get out and fly fish.
If I was on darby right know I would probably spin fish deeper holes.

I don't know the guy, but TheCream gave you some great advice. As a rule you won't catch a lot of fish in the winter, but for some reason some of the largest fish I catch are in the winter. Fly fishing is a sport that takes time to develop, but the rewards make it worthwhile. Sounds like your on the wright track. Good luck!