In your case, it seems an m3 is plenty good enough of a feature upgrade, I agree, no IQ differences are ever obvious here.
I just put this together for someone else: IMO:
There is no discernible IQ difference between any Sony rx100 for stills. So, it's about features,
m3: excellent IS, popup evf, tilt lcd, auto ISO in M
m4: 4k video
m5: hybrid AF combining PD and CD and faster AF and faster Continuous shooting.
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I moved up to m3, that's where I stay unless they put a hot shoe and mic port on one, then I would use the video for live music recording in small music clubs, school stuff.
four m3,4,5 features that give you shots un-achievable with the m1:
1. Excellent Image Stabilization. Now I can use P,A,M as well as S mode, getting blur free at 1/30th easily, if I concentrate, I can get 1/20th.
2. EVF. popup keeps the camera pocketable. Arms in, against your face is a much steadier shooting position than arms out lcd.
3. Tilt LCD. It not only helps with glare (as does the evf) it lets you take photos over heads in school activities, weddings, concerts, and helps take low shots, and selfies.
4. Auto ISO in Manual. Pick your speed, aperture, shoot. Light changes, cloud or branch moves, shoot, Camera keeps what you need and gives the best possible ISO for each condition.
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As for video, I want better sound, so I don't use video in my rx100's.
The mics are ok, but frequency limited, can get distorted by volume, and omni-directional, much unwanted sound. I use my old Sony Handyman, much more zoom, much better full range directional mic. It is not too big, and newer ones are more compact. It does HD, but I still use mp4, the video is quite good, easy to share, smaller files, etc.
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m5 Hybrid AF is definitely desirable, BUT, wanting and needing are different things.
The rx100 AF in the m1 and up to m4 is quite good already. People do not add an aside, like they do with the RX10's, or the RX1, wonderful camera but AF is slow, or misses too often. rx100 owners shoot and post. It is already fast enough for children running around. I used it successfully for kids soccer when I could walk the line staying close enough for it's short reach, it was fast enough. After the 1st season, the field gets bigger, they keep you further away from the lines, it's not enough reach no matter how fast or accurate.
Faster or more accurate for wildlife would be wonderful but with so little zoom, who is going to shoot wildlife with it?
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Continuous shooting, super fast, do you need it? Do you analyze golf swings, bullets thru oranges?
I shoot my Olympus Stylus 1 continuous for Ben's soccer games and now Cooper's Ice Hockey games and Ava starts softball tonight. rx100 does 4 fps. More than enough if close. Oly does 7 fps 300mm f2.8.
I wish I could slow my Oly down to 4 fps. The faster it shoots, the more images to edit, the longer it takes to write to buffer between sequences, (you might/will miss something better) lots of memory and more battery used. You may get a few great shots, and you may get the full approach and goal kick, but you can get that at 4 fps. It's the bright reach you need.