Does anyone happen to know the production numbers of the GRD4 vs, say, the GRD3? Finding a nice used one is tough, without paying an unrealistic premium. Is the demand really that much higher than the supply? I'm sure some people respond to the small-sensor advantage, but enough to move prices this far? The gap between GRD4 vs GR [APS-c] seems to have narrowed considerably. Or am I missing something?