I am going off topic, so I apologize right away.
Dealing with frozen shoulder for 2 years now and it's unknown when it will be back to normal...
Grabbing my 1DMk4 + 100-400 has been a real PITA and I am just glad that photography is just a hobby of mine.
I'd be keen to know how or what features you were looking for to pick Sony over another company and what this specific model made you go for it.
I don't know if I'd pick Sony for BIF, just yet. Tomorrow the alpha9 arrives and it might be the mirrorless equivalent of the 1DXii....I've done ok on occasion with
Sony for BIF, but never like I've done with the 7Dii or the 1DXii, but truthfully I've always shot BIF with Canon because I had the Canons. The a6500 is reported as being excellent for BIF but I only have the a6300
But the a99ii is a gem, an awesome melding of the A7Rii sensor with outstanding frame rates and it tracks wonderfully, IF you can afford the a-mount long glass. I can't, and make due
with the 70-400G2. The a99ii also has the DSLR like ergonomics that many like.
Problem is, with the a99ii if you did add the Sony a-mount 500mm it'd be just as heavy as the Canon kit
Maybe you saw this one, it was with the a99ii, and I got 15 frames all great of him coming in-
BUT if weight is an issue, an man oh man it is becoming so for me I'd look at mFT. At first many scoff at mFT for BIF but the new OMD M1 mk ii is another mFT beast entirely. Olympus did an outstanding job with many AF points and their tracking.
In my estimation it was the first mirrorless truly capable of BIF. Here are some of Poof's shots with the M1ii + 300/4-
Now Poof has been using Olympus for a long time. She'll tell ya this is the first Olympus she can shoot at ISO 3200 and relax about it. She's obviously better photog than me, I just have more gear, which shows all the gear and money don't beat the eye!
She'd also tell you that light and lots of it are very important for the mFT sensor.
It's still not like using a 7Dii/5Div/etc. but with the 300/4 or in my case the Pan-Leica 100-400, we can hold them all day, carry them all day, and live to tell the tale.
Now give me enough time (maybe August) and I'll be able to report on the a6300 and the new FE100-400. Supposedly this new Sony lens is sharper than the EOS 100-400ii, takes a 1.4TC. We'll see about all that.