Good question-and practical viewpoint. You're correct of course, a 'slick' pack works fine on developed trails.
Your parameters are specific enough to make honest recommendations.
Let me say up front that from the time I was issued the 'canadian ruck'[big knock-off Bergan design, steel frame with canvas bag] in '68 at Group at Bragg I've been fighting heavy rucks! [I was already a backpacker and thought most of the military stuff was truly 'retro']. Granted, a military ruck in an airborne unit takes a beating, there's no reason to accept that technology now.[And even then I carried a Gregory 'custom, handmade green nylon backpack with nice padding and aluminum stays when on non-jump team exercises.] I even used an 8X10 Eddie Bauer nylon tarp in Nam for night RON's and a nylon rain jacket rather than a poncho. So I don't think I've ever gotten locked into a 'rut' gearwise/institutionalized other than seeking the lightest strongest compromise with comfort and functionality possible. I say all that just to sorta establish some 'bona fides'-yep, I'm an ol' fart-probably older than Jim:-). [BUT I grew up on a horse ranch and not near the Smokies like him].
I recently addressed your question by buying a pack simply for 3 day trips in the Smokies. [NOT deep winter. After 3 chemo sessions and losing half my stomach I simply can't handle the caloric burn of cold, snow and weight-like Dirty Harry said, 'a man's gotta know his limitations'! No point in BS'ing oneself].
I got a Golite Quest, 4400 ci/73L [?] at 3#3 oz. at Sierra Trading Post -or maybe it was Backcountrygear.com-for about $125-great deal. I have mostly ultralight equipment BUT tend to take more 'snivel gear' than a true ultralight packer [again, I'm an ol' fart:-)]. I use the lightweight Patagonia waders and carry wading shoes outside the pack. [Waders go in a WP stuff bag inside]. My March Brown rod[s] either 7' [17" in case]or 9' [24
' in case]will fit outside or in. The Golite Odyessy at 5800 ci/95L is a better all around pack for what you suggest. Only weighs 7ozs. more and has compression straps to snug it up if not full. That's a minimal penalty to pay for the extra latitude. Considering most 5800 ci packs weigh over 6#'s alone, you're GTG.
For some perspective, the old steel framed/canvas Bergan weighs 6#'s as does the current military nylon version [but is bigger].
Let me also add this: an ultralight pack is a minimalist 'structure' compared to the more elaborate hipbelts and frame sheets/stays on a 6#+ 'AT thru hiking' pack. If you're carrying 50# + and busting *** to make 12-16 miles a day months on end, the 'hiking dedicated' pack is gonna be more comfortable. That type pack is designed for convenience to 'live out of' as opposed to a fishing ['carrying'] pack that needs to be acceptably comfortable and functional to move from car park to fishing stream site -probably only 5-6 miles, or even 13 ONCE until you go back DOWNHILL:-) a day or so later.
An argument I often get in with 'soldier wannabes' and pack selection is the weight/construction aspects. Neither they-nor a fisherman -needs a pack that'll sustain being dragged behind a deuce and a half nor creaming in from a broken drop-line on a DZ from 200ft. Nor do we need the 3 EXTRA yards of nylon webbing for MOLLE gear attachment-weight that does nothing FOR you. Practically speaking, if it doesn't contribute to your survival comfort and the REASON you're humping the gear to start with[fishing], it's extraneous BS-A WASTE. Not to mention a pain:-).
I mention that only to be kept in mind when sorting thru packs at the store [REI is pretty widespread and carries a broad selection of various brands/types of packs to compare. Any ultralight pack may feel 'light'/flimsy? compared to expedition packs. Simply keep in mind, it's gonna be on YOUR back-how much abuse do you intend to put YOURSELF thru to be worried about some nylon:-)]. Packing the inside of an ultralight pack bears thinking/planning about for ultimate comfort-it's easy and plenty of info. is available.
Hope I haven't put you to sleep, BRF-I do go on in my dotage:-). Feel free to ask if I've muddled something. http://www.rei.com/product/781547