Generally the lighter the line the less resitance to the fish both in visbility and tension. Probelm is the ability to land good size fish. Fireline helps cause it genrally holds great feel and punches well above its marked weight.
Question is what type of fishing are you looking to do?
If its table fish, like bream, flatties, whiting etc... then 4lb with some good fluro carbon leader in combination with a good drag, will go nicely.