Depends on 1) temp of the kegerator, 2) length of the tap line, and 3) style of beer and desired volumes of CO2.
Assuming your tap-line length is typical, and assuming a typical carb of ~2.5 vols at typical kegerator temps, you'll want to dispense at 10-12 psi. Under these assumptions, 5 psi would only be useful for an extremely cold imperial stout.
My kegerator temp is set to 37F and I keep the regulator at 9-10 psi. My kegs have very short lifespans and so I do not worry about slight over/under-carbonation.