I'm not a CCD engineer, but I suspect you're both right. Photon shot noise increases like the square root of the area of the pixel, but the signal will increas

I'm not a CCD engineer, but I suspect you're both right. Photon shot noise increases like the square root of the area of the pixel, but the signal will increase like the area. In that case, the important quantity ( Signal/Noise ) improves like the square root of the area of each pixel. If readout isn't shot-noise limited, then the payoff for a larger sensor could be as large as the ratio of the areas between old and new.