I think in Tournament Poker for advanced players by Sklansky, he says that a tournament pro could have up to a 5X (500% ROI) edge on the competition (maybe I'm not remembering correctly though). I think this is likely true in live play with generous blind structures. I've played in a few live tourneys and people either suck or have no idea how to adjust to tournaments as most of the better/tight players are way too tight.

In online tourneys I think that your edge is likely decrease due to the fact that overall the blinds escalate a little more quickly, and the play is more aggressive, and overall the play is a little better. But I would guess that a 2+2'er should still have at least a 1.5-2X edge over the competition (50-100% ROI). That's just kind of ballpark figure and could easily be more or less. But I have not played a ton of the bigger buyin events so your edge might not be quite as good there. I think the rest of your questions could easily be answered if you knew what kind of edge you have, but I think that you're never going to play enough tourneys to know what your edge truly is.