If you mean IBIS, then the a6500 does have in body stabilization I believe, unlike the A6300.

Did you use the adapter on a 6300 or 6500 camera? How long ago was this? I am just wondering if a recent adapter would work slower on a a6500 than the lens would work natively on the A77? Are there other downsides to an adapter in term of IQ or f stops?

But it's full-frame isn't it? That is not the direction I want to go as a 70-400 would only be a 70-400. I want it to be 105-600 for taking pictures of distant ships.

Weather-sealing would be good. All three cameras seem to be weather-sealed to some degree, but the Sony lens apparently is not, while the Nikon lens seems to be. Correct?

I hope I have my facts straight. I am considering going the Sony route. My photography is pretty much limited to sea-going vessels (container ships, bulk carriers, tankers, military, tugs etc) and secondarily birds. Therefore, I prefer the APS-C sensor because I often need all the telephoto I can get. The lens I am most interested in is the Sony 70-400 that seems to come only as an a-mount. The a6500 is an e-mount camera with a adapter available for a-mount lenses. The A77 uses the a-mount natively. Does the adapter have disadvantages over a native a-mount camera? Are there considerations other than smaller size mirror-less versus conventional camera that I should be aware of? Not sure I will go this route, as the Nikon 80-400mm plus D500 is also appealing but more expensive.

everyone a marketing department describes in glowing detail.

Well, not if you are a veteran or newbie willing to put in some research. You can figure out what the level of capabilities are. But if you are fairly new to photography equipment or have been content with a film camera until recently, it is not always easy to know which models you should be investigating. I often try to use the DP Review side by side comparison table - but I keep having to do that as I read about some camera that someone likes or I see a good Ebay price because I can often not remember what the model numbers imply. But thanks to several responders to this thread, NOW I do have a much clearer idea of what model numbers mean for Canon & Nikon. Now Sony...

It's making more sense now, but I am going to have to make a cheat-sheet to remind me.

Interesting: 3 digits entry; 2 digits better; 1 digit best. Thanks, that makes a bit of sense, though I think it would make more sense nowadays to further consistently differentiate models by sensor size and mirror/mirrorless some way.

Is there any rhyme or reason to the way Canon and Nikon make up model names? I mean, for example, the 5D & 6D Canon are full frame yet the 7D is a crop sensor. I just am bewildered by all the model names and trying to even figure out which ones I should be interested in. I own or have owned both Canon & Nikon but the marketing names have always puzzled me. Is there a reason why the Nikon D500 is so named versus the D7200 for example?