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If you are having to dial the preload more than 2 to get the right sag you're not on the right spring. Buying a longer spring and cranking the preload because you don't want to buy another spring is not the solution. Terrible audio but here you go. https://www.youtube.com/watch?v=uUGRbaWlH8M

You should have gone up a spring rate. Page one of the setup guide for the shock you used said if you cant get the right sag from two preload turns then you need to go up to the next spring rate. What you did by adding preload was take away from small bump by increasing the force required to move the spring at the beginning.

Changing from 2.75 to a 3.0 should have no impact other than being heavier if you are running the same spring rate (400# or whatever it is) That 2.75 just means it's the most the spring can compress before it binds. That 2.75 or 3.0 # must be = or be greater than the stroke length on your shock to avoid binding. Ie 2.5 stroke length can take a 2.5 or greater spring but only to the point that the spring will actually fit on the shock itself. There is no point in going more than what the stoke length...