When copter is not foldable, size matters.
Diameter for my Y6 is 700mm, it will be 900mm with the same propellers and a slight tip clearance.
More arms, longer arms, larger center plates to accommodate more arms = more weight.
Y6 apparent surface is less important than true Hexa (1/2 ratio). It may need more power to fly.
Upper and lower motors can have a difference in efficiency. It is true on my Y6 (maybe 10% difference) but false on my OctoQuadX, all motors have quite the same PWM when in loiter mode.
Clear field of view is wider with the Y configuration.