In most GUI's knobs behave like faders, just with a different virtual taper.
I'd prefer a round *display* - I don't care if it's called a "knob" or "fader"- reality is you do similar movements with the mouse anyhow... So to me, the important aspect is (once again)...
HOW SCREEN SPACE IS UTILIZED.
I think a smaller round "knob" that has a very bold arrow (ala Ableton) that indicates the panning would be better. But I would still want the taper to be like the fader is now with cntrl held down.