imo a properly tuned gun will shoot the same regardless of the barrel length. my p90 at 247mm barrel shoots just as accurately as my g36 with a 407mm barrel. both are the same bore diameter.
At 1.5J (400fps with .2g BB or 326~ with .3g) the 2 guns will reach out easily to a man sized target 60 meters. At that point I lose sight of the BB. But my guns are not anywhere near off the shelf models.
Barrel width and length are not as important in airsoft ballistics as the consistency of the bore... so a high quality barrel with a super smooth bore will get more accuracy at any length.
Any gun can be tuned to any FPS or rate of fire you desire, so it comes down to which gun do you feel most comfortable lugging around.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.