First of all - I love my A6400 and plan to keep shooting with it in tandem with the new A6600 which has just arrived. I will often photograph over a hundred dogs a year for Maltese Rescue California and the Animal Eye-AF of both these cameras is nothing short of outstanding. The small form factor of each of these cameras combined with Animal Eye-AF makes it easier to shoot one handed while I am offering the dog treats with the other hand. The full time Eye-AF makes it a snap to photograph people with the eyes in focus...
I bought the A6600 when it went on sale at Adorama for $1,200 U.S. Dollars with a decent kit of accessories including a good (Godox/Flashpoint TT350) flash and a very decent SD card among other things...
Here are a few parameters of the A6600 which I really love. I have numbered them in their importance to me personally in my style of shooting. Other photographers would certainly list them in a different order and may leave some out or add others...
1. LARGER GRIP... The grip of the A6600 is significantly larger than any other A6xxx series camera in order to fit the Z battery. The larger grip is a lot more comfortable to hold than the smaller grips of the previous A6xxx cameras. This is especially beneficial when shooting one handed (see #1 above) and/or when shooting with a slightly larger lens such as the Tamron 28-75mm f.2.8 or the Sony 70-350mm f/4.5-5.6. The grip of previous A6xxx cameras cam be modified with wood additions to make the hand hold easier.
2. ISO 50... This has not been addressed by any reviewer that I have noticed. I really like the ISO 50 capability of the A6600. The top shutter speed of any A6xxx camera is 1/4000 second which sometimes is too slow when I want to shoot wide open with a very fast lens in bright conditions using ISO 100 which is the lowest ISO of previous A6xxx cameras.. I have often wished that I had the advantage of 1/8000 second shutter speed. However, the ISO 50 capability should often allow decent exposure wide open at 1/4000 second. This ISO also makes using a very slow shutter speed sometimes feasible without an ND filter.
3. EASIER REMOVAL REPLACEMENT OF SD CARD... The larger Z battery allows space for positioning the SD card slot in a location that makes it easier to remove and replace the card.
4. IBIS... Since I don't shoot video, the lack of IBIS in the A6400 is not a deal breaker for me. However, it is nice to have when I am shooting with non-OSS lenses or when I am shooting hand-held with the 70-350mm f/4.5-5.6 G OSS lens. I have not yet ascertained just how slow I can shoot using the IBIS/OSS combination but, in early trials it seems that I can effectively hand hold at slower shutter speeds than with the OSS lens and a non-IBIS A6400.
5. GREATER BATTERY CAPACITY... Again, I am not a video shooter so the relatively low capacity of the FW50 batteries of the previous A6xxx series cameras has not impacted on my shooting to any great degree. I always carry extra batteries and my Meike battery grip for the A6400 will provide just about equal battery capacity...
6. TWO ADDITIONAL CUSTOM BUTTONS... The C3 and C4 custom buttons allow even more customization of the A6600
I also love the A6400 but, the only thing about it that I like better than the A6600 is the lower price which has been somewhat mitigated by the recent $200 reduction of the A6600 selling price...


