I sight in 2.5" high at 100yds; that get me out to 300yds with little or no holdover. Having said that, most of my shots are close range so even 2.5 is overkill and I doubt I would take a 300yd shot anyway.

2.5" high @ 100yds is just a good rule of thumb to me. Less may even be better but more would just increase my probability for error.