[davidmanze]

I don't know much about Sony APS-C bodies. What are the main differences between the A6500 and A6600?

As far as I know (see https://www.dpreview.com/products/compar...sony_a6600)

1. Boosted ISO 102400 on the a6600 vs 51200
   
2. No built-in flash on the a6600
   
3. Less video modes on the a6600 (some variants with limited bandwidth, a6600 has got all the hi-quality stuff)
   
4. USB charging on the a6600
   
5. Headphone port on the a6600
   
6. the a6600 is 50 g. heavier
   
7. the a6600 has got timelapse recording.
   
8. And the mentioned battery thing.
   

So nothing relevant for me. Well, timelapse might be interesting, but in the end I've done this only a handful of times in twenty years, so...).

 
  For me it's simple, I've been following the A6000 series as the models came out ..

...... the two main criteria as far as I'm concerned are; ....... the AF tracking with all it's bells and whistles including the automatic eye/ face/object tracking which now forms the basis of Sony's later A7 series ...... where the camera finds it all automatically and which Canon went on to develop with the R5/R6 ...... that only exists in the A6400 and the latest A6600 ....... I would absolutely want that!  ....... 
 ..........other models are pre-Sony AF revolution ........

..... and the other being: ...... IBIS, the A6300 (older AF system) has it, as does the A6500 ...... however, the A6400 does not ........ IBIS IMHO is also a total must have ....... which rules out the A6400 ......

....... in fact the only camera that have those two features is the A6600 ....... and a whole bunch of other stuff which you have mentioned ..... 

 So that would be my choice as the camera I would be choosing if I was looking for one of the A6000 series camera ..... 

 ... the A6600 has it all !......

As always Sony went with micro incremental updates through a series of six bodies before finally nailing it ........ shrewd huh ??

....... a nice little tickle as they say in England .......