It is a real Zeiss lens not optical zoom. It has optical zoom but I never tried it.
It is a big Zeiss lens. The RX10 I and II were very popular for video etc. They had 24 to 200 lens and constant aperture with
built in ND filter. The III lost the ND filter and constant aperture. But the lens is astounding good at most ranges online many zooms.
The newest model of the camera has improved the AF and is even better.

You can do anything with this camera. I sat in a stage presentation my son was one of the guests onstage in the audience hand held
and shot different zooms to create a video of the whole show. Never got out of my seat. I shoot soccer games with this camera
and it works great. You need longer reach and I never worry about a shot across the field. I have a good 70 200 cannot do what this
bridge camera can do.

You may be confusing Optical zoom (through the lens with the whole sensor) with Digital zoom (cropped in to part of the sensor). Yes, the Zeiss lens on the Sony RX10 actually does optical zoom with an equivalent 24-600mm onto a 1" sensor; this lens is very sharp. Beyond that it can add digital zoom (cropping) for even closer shots at lower megapixels. I have the RX10 iii, but would love to have the RX10 iv for its much faster autofocus. Also, you can focus on things as close as 1 cm with the lens at it widest. The only weakness of this camera is the 1" sensor is only moderately good in dim light.
[edit] I too have never bothered with the digital zoom on this camera.

I don't know anything about the Sigmas other than they usually get great reviews. The 120-300 should be all you would need for your sports. It may be a little long for indoor hockey depending on how big the arena is and whether you decide to go with the FF. It will be really long indoors on a crop. In reality, I get along with a 70-200 for baseball on a FF so if you are shooting on a crop it would be plenty for that.

As far as the 100-400 f4.5 to 5.6, I had the same f stop range in the 70-300 Canon L. I sold it and got the 70-200 f2.8 because it just didn't have enough light for indoor shooting.

One advantage of a FF in the 5d Mk4 or the 1DX is you are able to bump the ISO considerably higher than you can with a crop frame.

By the way, until you brought it up, I was not aware of the Sigma 120-300 so my wife will quite possibly be really pissed at you.



Bill