I would think that taking off would be easier for Cadence since she's so much lighter. The heavier you are, the more power you need to get off the ground. I would think that Celestia would need a running take-off.
The little details. Oh, gods the little details. You manage to make it seem so much more real without compromising the show proportions. Fetlocks, muscle lines, bone protrusions, general shadings. I am a stickler for little details. Do the maths.