ive read somewhere so take this with a pinch of salt, that a pb's acceleration is optimum after 6". so the remaining length of the barrel will add or decrease properties to the flightpath. (spiral/straight porting, friction, noise reduction, bla bla...).
remember that to much isnt always better, ive got a 21" spyder barrel thought it'll be fun. it is cack. it suffers from the markers vibrations, it is bulky and hard to move with. and it makes my balls drop a lot shorter than what cold water and strong wind could ever do to my other balls.
so yeah basically there isnt really too great a need to go above 14 or below 12. but there are some nifty tricks to pull off with a 16" and dont have to be done during dutch sex shows, although i wouldnt mind seeing some.
for example indenting supair bunkers with your 16" barrel so you can get greater field of fire whilst keeping as tight as a ten year olds bum is one, and runnig the rims of the tyred bunkers of speedball fields. just buy quality kit. and take note from the last poster. plus if you want that extra bit of range, then try taking a few steps forward.
buy good paint and maintain your gun, these are the best improvements of accuracey.