I haven't done much with the Power Ponies since I started making art of Cataclysm and Armageddon. Let me fix that...
I decided it would be fun to have all of the Power Ponies have different body types. I'd already shown that a little bit with Glory and Feathers, but not so much for the rest. So here's a height chart, with the line representing the height of an average pony (not counting the horn, ears, or wings).
Galaxy Star: Average height, average weight. Basically like the ponies you see in the canon.
Clever Comet: She's the youngest of the Power Ponies, and as such is ever so slightly shorter than the average adult. She's also fairly lean.
Sky Song: Average height. She has a larger ribcage, giving her lungs more room. Which is great, since her special talent is singing.
Azure Glory: About half a head taller than the average mare, and very thin as well, with a long horn and ears to match.
Buttercup Cottonwood: A full head taller than other ponies, because she's half-horse. She has a very muscular build, and a muzzle just a few shades lighter than the rest of her coat.
Feather Fluff: I retconned Feathers into a hippalectryon (which, for those who don't know, is basically a chicken-hippogriff in reverse, although Feathers here has hummingbird traits instead). Because why not. She's very tiny - half a head shorter than most ponies her age, and skinnier too. Not that it matters when she's angry...