Spriter ?
The plugin is coming for C2 and so you'll be able to have far more control over the animations and characters than the bones behavior could offer.
As for an implementation working now, I guess sprites + pin + XML that holds all the positions/angles/size of the "keyframes" and lerping through these informations between the keyframes is the way to go.
But that's pretty much what Spriter does, I guess it's worth waiting for it.
Edit: also yes, good FPS on my PC too, it's working smoothly as intended.