Don't worry about your 8 weight rod being too heavy, I have an Orvis Trident 8-9 weight and that is what I learned with, fishing for 6 - 10" Brookies in the streams around southern Maine. Just make sure you have a tapered leader, either purchase one or tie up your own, starting heavy and reducing size every 3 feet or so until you are down to your desired size. Leave the 8 weight line on, dedawg1149 is correct, you will only sacrifice casting ability. Let the leader dictact the size. The only draw back is that a 4 weight makes it seem more intense.
Streamer flies...... there are tiny gray ghosts that I would use (size 8 or 10 single hook or so?), a small Montreal would be great. Mickey Finns are popular and available in tons of sizes.
Dry Flies..... Stimulator is what I would lead with in the fall, nice colorful fly. Should drive the Rainbows nuts! Elk Hair Caddis and such might work.
Nymphs..... Hares Ear or Prince (beaded). Can even drop a tiny one off a Dry Fly connecting the two with a couple feet of tipet material. Dry Fly acts like a strike indicator, tho the Bow could take either or.
Wet Flys..... kind of like streamers, but I have a home grown Horn Special that slays 'em. Look for a small Hornberg.... simular in design and deadly when twitched.
Probably want to cast upstream and let a nymph bounce along the bottom down past you. I doubt you'll see much surface activity this time of year, but you never know.
Don't forget about twitching that Hornberg thru the current!!!