Longer Barrels will NOT increase your range. Every marker is chronied at 280 feet per second, which means that in 1 second, balls from any marker will travel 280 feet (actually not a full 280 because the ball will decelerate, but 280 is good enough for this thread). The tippmann flatline will put backspin on the ball, giving it lift thus letting it fly further, but this is a different effect than simply a longer barrel.
As for lengths for players, as far as sup air is concerned, any player can use a long barrel to manipulate a bunker. What it comes down to is player preference. There is no "back player" length or "front player" length. I have played both on different teams and have used the same barrel for each (its a mere 12 inches but its what I'm comfortable with so its the best barrel for me).
Hope this helps