> But said 3D context makes use of modern hardware and not some 2D accelerator that hasn't seen any significant improvement for nearly a decade.

You misunderstand me: some operations are faster even despite a modern 3D accelerator. Uploading textures and/or scene setup isn't cheap, and depending on what you do in a 2D context, this can cut out any benefit you might have seen.

Unless you're blending or parallaxing like no tomorrow, I just don't see any real advantage of using OpenGL as a backend. If Arc is a nicer or more portable library, right on, but performance?

Of course, hardware changes, and maybe I'm behind the times. I'd love to hear something more substantial regarding this issue.