my $0.02=
the 14"is the one i have.buddies have the 10's and the 12's.shot pattern does not chande with any of the barrel lenhgts,just the muzzle blast of the 10 can be annoying.
i prefer a 4 shot load.seems the 6 and even the 7.5's have no balls to get threw even the slightest peice of brush.
will kill/hit rabbits out to 20 yards/after that you may need a dog to get the game run down,it will be hit but sometimes not dead.
here are some clips of me/us.you can veiw all our pics at
http://s200.photobucket.com/albums/aa95/madcatter69/

these are some i threw together to show ya how i use my 410