I use a 3wt most of the time when 'gills, crappie, and small bass are likely species.
I find that all 3wt rods are NOT created equal, though.
My 6'6" Lamiglas 3wt (custom rod on 3wt Lamiglas blank) is more like a 1wt with my casting "stroke". I usually line it with a wf1f or dt2f line depending on what casting conditions I expect (overhead or roll cast).
My 8'6" Ross Essence FS is more like a 4wt with my "stroke". I can cast a wf3f line, but a wf4f fits my casting style better.
I recently cast a 7'6" TFO Lefty Kreh Signature rod and found it to perform more like a true 3wt in my hands. The wf3f line the owner had on it allowed me to feel the rod load to perfection (no peeking at the backcast necessary) and the accuracy I had with it was superb.
(MY new TFO rod of the same length & model should be delivered tomorrow
All those rods work fine for the species mentioned, but the Lamiglas makes a 10" bluegill feel like I've hooked into a monster. The Ross is fun, too, but a 10" gill doesn't make me worry the cork is going to explode on the next run.
Didn't hook into anything bigger than 8" or so with the TFO when I used it, but it felt like the 8" fish were putting up a good fight and it was a job to keep them from diving into the weeds.
I tried a Redington CT earlier this spring and found it to be similar to the Lamiglas in my hands. A bit faster, but still a full flex blank. Since I like the Lamiglas (and trust the glass blank to be durable) I decided to sell the Redington and keep the Lamiglas for those locations where that action serves me best.
For me, the length of the rod is a factor in distance, but not a huge factor. Just guessing (never actually measured), but I'd estimate the length to distance ratio is somewhat proportional for me. If I get 40' with a 7'6" rod I'll get close to 35' with a 6'6" rod (about 88%) and 45' with 8'6" (about 113%).