Is the G85 decent under low lighting?
Let's put this in context.. you mean you want to shoot in available or existing light situations and you don't want to use flash ?
This means you should understand about exposure and it's relationship to shutter speed,aperture and ISO (image sensor sensivity).
In the old film days people have ISO (it was known as ASA) to graple with at maximum it was only ASA400 that was available and you have aperture and shutter speed to play with.Even then in low light senario people have to expose as if it was a higher ISO and then delvelop the film known as push processing (playing with developing time and exposure characteristics of film).Of course the result is not pretty as there is film grain or photo looks grainy when printed on photographic paper. Now in digital photography although low light photography is easy as increasing ISO which some cameras can go over ISO 500,000 the result is similar to film grain except
technically it is now called digital noise but it is rather improved as good performance can be had at ISO3200 -6400.
So I don't think this is an issue if you have such a camera...a great improvement over film cameras.
All 3 cameras you have short listed can do low light with a combination of a fast lens eg. F1.8 and ISO with image stabalisation
even with low shutter speeds. All now you need to know how to steady yourself with tripod or hold your camera properly
and most importantly use whatever light sources available ,natural or artificial in your composition. You have much flexibility
now with digital cameras.I don't know why people keep harping on fast lenses,yes it's convenient but you have to contend with shallow
depth of field and don't be lulled as taking portrait of a face you may have focused on the nose or some other feature and the photo
does not turn out nice because of blur.Even autofocus is not foolproof.Back to basics.As a matter of fact not many photos are shot at maximum aperture for technical reasons..subject isolation is good but sharpness across the frame suffers if you are using normal
or consumer grade lenses. Hope this helps.