What I look for in a Canon compact.

Actually the original M itself is quite capable; it's just the default exposure it, not smart, and you need to shoot RAW which on the original M, is downright poor performance in terms of FPS capable. I don't know if the original M has highlight tone priority, but if it does, use it and shoot RAW. That'll give you a lot right off the bat, no purchase needed. BTW, I think the PowerShot S100 may support this too, have a look. Give your PowerShot and your original M some more oomph. Should also add, processing these in a modern post processor gives noise reduction a substantial lift over in-camera JPEG too. Both DPP4 (free) and other post processors help. Now again, RAW performance on those cameras is slow, maybe 1 FPS though.

I'm going to side with KEG and say, M200 and M50 are huge lifts over the original M.

Also, the M5, M6, M100, all also share ADC on sensor. You need not go all the way to the latest and greatest. DIGIC7 and the 80D sensor goes a long ways. I do recommend an M200, M50 or M6 II though just so you get DIGIC8; much better AF.

The G1X Mark III itself uses the 80D sensor (ADC onboard) and DIGIC7. It's worth a shout if you want to stay in the PowerShot family. It really is cooking if you ask me. I've shot both the G5X II and G1X III, and I'll say, it really depends what you want to do. Both give unique benefits. I personally favor the G1X III, but, the G5X II's lens is really something with it's reach and speed (aperture).

The G1X III though on the other hand just has more image quality. It is APS-C after all. No way around it, more resolution, more color accuracy. Coin toss.