Christopher,
I only owned the RX100i for a week before I had to return it due to some mechanical issues. I’m not overly qualified to compare it to the A6000 I’ve owned for a couple years now.
If all you were interested in was still photography, there’d be little reason to upgrade from the A6000 (unless you feel five axis in body stabilization is worth a near $1000 price increase to go with the A6500). Edit to add: There are increased opportunities to adapt lenses and use auto focus on the A6300/A6500 that you can’t with the A6000 due to firmware issues. Plus you can use an external charger with the A6300/A6500 during long timelapse shoots which you can’t do (easily) with the A6000. Also, there’s a notable performance improvement with the buffer of the A6500 over its predecessors. For me, these aren’t features I’m willing to pursue at a $1000 premium but your needs may be different than mine.
It appears that you’re interested in the video performance on the A6XXX line, and I can give a little insight on that.
Sony has a real overheating problem with their A6xxx line that they failed to remedy with the A6500. There are a few things you can do to mitigate this, and the A6500 has a setting where it will allow you to continue shooting video when the temperature sensor would’ve shut down the A6000/A6300, but it’s still a real problem.
Once you hit that wall, you are sitting there with a brick in your hand until it cools down again. I’ve had my A6000 overheat on me in a climate controlled 70*F auditorium after only 15 minutes of 30fps video at 1080. Shooting 4k at higher frame rates will only make this problem worse.
I’m personally going to buy a Lumix G85 for my video work. It has a smaller M4/3 sensor, and auto focus and low light performance isn’t quite as good as the A6300. For me, I’d rather get the shot that has a little noise in it or have the camera search for focus occasionally (I’d default to manual focus on a static target anyways), than miss the shot entirely because I’m waiting for my camera to cool down.
If I didn’t think I’d shoot more than five minutes at a time, then I’d upgrade to the A6500. But, I do want to have the ability to film interviews and concerts, so I’ve written off the A6xxx line until they fix this issue.
It’s my hope that Sony will someday release a prosumer APSC camera that has a large enough heat sink to handle the video work, two SD card slots, and a headphone jack. Until then, the G85 (possibly G7… or the new G5) looks like the direction I want to go.
Edit to add: It’s also worth mentioning that the Sony A6xxxs are notoriously inconsistent with this issue. Max Yuryev and Jordan Drake got their hands on a few A6500s and compared them to the A6300 and the results were all over the map. I’ve compared my findings with the A6000 with other A6000 users, and some are doing much better, and others are doing much worse.