I think the Note 4 will have a 5.9" screen (assuming they follow the same .2" increase with each Note iteration). I also think they'll keep the overall size down, like they did with the Note 3 (virtually the same size as the Note 2), by reducing the bezels.
I'm on the fence though if the Note 4 will have on screen buttons because that would effectively cut the screen size back down near Note 3 levels unless when in full screen or where the buttons are not shown. But that's a minority of the time, thus why I'm apprehensive about them.