The colder the temperature the lower the pressure you need to maintain carbonation. For example, a keg held at 35 degrees with 10psi of applied pressure will have the same carbonation rate as a keg held at 43 degrees with 15 psi of applied pressure.
So to set your system, you need to figure out at what temperature you like your beer, adjust the carbonation to the level you desire, and then find the right line length that provides the correct resistance.
The rule of thumb for balancing systems:
Lbs. of applied pressure = the total pounds of resistance supplied by the beer line.