As the background of what mordantly just said, in case you aren't aware, you want to "balance" your lines. The flow resistance of the line should equal or exceed the CO2 pressure at which you serve, using figures such as those he posted.
so if I have 5' 1/4" lines I'd have to run the pressure at 3.5 lbs?
You want to figure out your desired carbonation level first, then calculate how much line length you need to get a proper pour at that pressure. Your beer will be pretty flat at only 3.5 psi, but it'd probably pour nicely.