I would expect Text Kit (I assume that's what you are referring to by typography engine) to seriously out perform Web Kit on older hardware, such as iPad 2. UI

I would expect Text Kit (I assume that's what you are referring to by typography engine) to seriously out perform Web Kit on older hardware, such as iPad 2. UITextView with Web Kit backing has to do so much shit just to render attributed strings. It's slow as hell. Text Kit provides a clean layering atop Core Text with a fast way to update the model.