Anything past 500mm focal length atmospheric turbulence can be detected. A night with a steady atmosphere is really needed.
That looks pretty darn crisp to me.This is my first image with the new G3x. I don't have the settings figured out yet, so this was one of several single shots (no burst mode since I haven't gotten that far). Interestingly, all shots had equal sharpness or close enough that there wasn't an obvious difference between them at 100 percent view. This was JPEG only, and my photo editor is the 1998 edition of Paint Shop Pro, so there's very little magic here except for some gamma/curves applied along with some crude sharpening. Considering the number of steps I did in PP here, the noise is very good. And since I didn't have a solid support, I'd say the IS is extremely good.
Canon G3x at max. zoom, f5.6, 1/200 handheld/braced, ISO 200.