Length will depend on how it is used...longer for dry fly presentation and/or belly boat/toons, shorter for walking up the little creeks....
If you are packing into high lakes, the 4 pc. makes sense, but its tough to find a 3 wt. in anything but a 2 pc... so theres your quandry...
I know on the creeks my little 6 ft. 3 wt. gets me long enough casts ( up to 30 ft.) and anything bigger than about 14 inches on it turns into a rodeo...
I just like light tackle.....
Ingwe

"...the left considers you vermin, and they'll kill you given the chance..." Bristoe