ED is about as far out of London as I want to move (ideally, I'd choose to be a bit closer, but in ED you get 'nicer' for your money). It is just about comfortable cycling distance (i.e. under 30 minutes without breaking too much of a sweat). Once you start getting into zone 3 / 4, I kind of think that the benefits of being 'in town' significantly reduce - you may as well move out properly, somewhere on a fast train line and get more space and more greenery.