When is a bike too high?

It might seem a stupid question as preference and rider ability should play a role I suppose. I have an itch or call for another bike, but I am concerned with that bike's height, especially in more technical terrain. On my 800 both feet reaches flat on the ground, but on the one I would like to have only a bit more than my toes reaches the ground. At a slight slope I might be in trouble. What is the recommended touch one should have, like I said especially when not on tar / technical.