I think I heard once that all level 50 items(not the nodes; the item itself) cannot be brought to a 100% gather rate with the gathering stat alone. I think the max is 95%?

As for level 49 items or below, you probably need a fair amount to hit 100% because having "on-level" equipment at the level it's obtainable usually gives a gather rate of about 80%, and you cannot surpass things this time with higher level equipment but with materia instead.