you can do your fps as you like. the main spect is the realism of your game. the "old-school" shooters are not quite realistic. so you just have your cross-hair staying in its size and a given accuracy. the older shooters have the princip to just shoot everything that comes into your way! i like that style! :-D
soldier of fortune I, quake 2, unreal I were quite nice games where you can fetch some ideas. good luck