Excellent article comparing the two current E-M10 generations, thanks!
There are a few more differences between the Mark III and Mark IV that might help people trying to choose between them.
The Mark IV has returned a very useful feature that the E-M10 Mark III lost (which had been present on the earlier Mark II version): you are free to select silent shutter in the program, aperture priority, shutter priority and manual (PASM) exposure modes, giving more useful flexibility in its use. On the Mark III, the silent shutter was only available in the Silent Photography mode on the AP dial position (which the Mark IV also retains, for those who still want to use it that way) - that version is more limited because it is program-only and also has many configurations and settings disabled for simplicity.
The Mark IV's setup menu contains the ability to enable TTL electronic flash with the silent shutter. For current interchangeable lens mirrorless cameras, this is a feature unique to Olympus. The maximum flash sync speed is a slow 1/20 (only when using silent shutter - it is the normal fast speed with mechanical), but it can still be useful at times Incidentally, this is also the case with the Olympus Pen E-PL10, which despite being a 16MP camera, has all the same features regarding silent shutter as the E-M10 Mark IV - and similarly the previous E-PL9 had the same limitations as the E-M10 Mark III. The more expensive current Olympus models with 20MP PDAF sensors can sync electronic flash with silent shutter to 1/50, which is more useful still (the now-discontinued Pen-F had these features too, but was also limited to 1/20 sec flash sync in silent shutter - this makes me suspect the E-M10 Mark IV in fact uses the Pen-F image sensor, as it too used CDAF).
Another feature new to Olympus with the E-M10 Mark IV (and again, also the E-PL10) is fully in-camera panorama shooting - previous Olympus models could shoot panoramas but they needed to be assembled in software afterwards. These two models can do it in camera, with an option to shoot even wider panoramas if required. Many other brands have had such a feature for a long time, but many of their models seem to be losing the feature nowadays. It's a fun feature and quite likely of interest to prospective owners.