For me depends on the water, load, mood etc. as this changes the tab and trim settings. I would interpret it as the sweet spot where you can feel the hull just coming up on top and the engine is not really working that hard. Should be close to optimal fuel economy as well. In my case somewhere between 2900 and 3200. I know some that just run em all day at 4300 and call that cruise. The fat boats seem to run along at 2200 and don't have a clue that they are not on plane as they throw a wake that totally hoses the river for a mile.
Good question, probably also depends on the budget for the year!