I attended various talks by Ben & Casey at Eyeo, and they mentioned the new 2.0 series of Processing including a lot of great new OpenGL improvements by Andres and others, and that the new GL framework shows performance near OF. In another talk, Ben mentioned prototyping something in Processing, and then porting it to OF for speed.

I'd say that in general we'll see this all matter less and less, what with more GPU type stuff happening, and with the advancements in the JIT and code translation in general.

For computation-heavy apps, probably. For others it'd probably come down to something at the framework level, such as the efficiency of the OpenGL bindings or event/callback infrastructure.