It depends on what for you get. If you get the same fork with 5mm more travel (ie 04 vs 05 Vanilla), you won't notice it. If you replace say an 04 Vanilla with an 04 or 05 Marzocchi, you'll definatelly will feel the difference because of a taller axle to crown height on a zoke. Basically, check AC height of the fork, especially it's sagged, or riding position AC, 5-10mm of difference will probably go unnoticed, anything more will make it noticable slower or twitchier, depending on which way you go.
_MK