Didn't think you'd be able to shoot as low a shutter speed as that. Stabilisers must be quite effective. What ISOs/body do you use then as it doesn't look like an extreme ISO.
I wonder how good the new Olympus sensor with its 5 point stabilisation would be for your work and if you used a metabones speed booster with your Canon lenses that would also give you some extra light. I wonder if that would outweigh the small sensor Vs your Canon sensor.
1DX, it's very usable at 12800iso if you want. I've found it works well just to use multi pattern metering, it then is probably over exposing. The raws are as flat as a flat thing. It was also a windy night which didn't help.
I use to think I wanted the raw to look close to the final image, so I often knocked a stop or two off the metered.
Over exposing I have lots of control over the shadows, the highlights hold as well. They are all processed in Aperture, no noise reduction added. I have Ninja, but honestly I prefer grain and detail to smooth with the edge off.
I think I got up to either 6k or 8k. It's a lot darker than it looks, well after Sunset for most of them.
The weather even at night makes a big difference, cloudy nights act like a reflector, reflecting all the city lights back. I actually prefer clear nights and a good Moon, if I get the choice.
Night aerials it depends on how much fill you want to record, the city lights are a constant, your exposure is just for the fill really without blowing to many highlights.
Film days I was limited to 800iso, so I shot at 1/30th at f2.8, no choice.
I know this goes against the herd, but I shot the Nikon 800, D4 and 1DX against each other at high iso in my kitchen, the 1DX won. All those pixels offered less resolution at high iso, the D4 and 1DX were neck and neck, the 1DX had a few more pixels which gave it a edge, small but there.
I've shot the 1DX on an air to air shoot in bad weather, it was still capable of being quick enough to give me a 4 image stitch of the target aircraft and extended City background.