For those of you who use this lens (C or S) for birding AND utilized the USB Dock to custom set, which custom AF setting have you found more effective: FAST AF PRIORITY or STANDARD AF?
If FAST AF PRIORITY, have you experienced any noticeable drop in AF accuracy?
Do you use the settings alternatively depending on whether it's BIF or bird portraiture?
Just got this lens the other day and when out for testing yesterday using the lens' default AF setting. Although successful and I was quite pleased with the lens, I lost quite a bit of good shots due to its sluggish AF hunting. So I'm wondering about your experience with the different settings. I want to go out and find it out by myself, but the weather isn't cooperating.

I just got the Sigma 150-600 S for birding as well, I have the dock as well. So also interested in user experience. Using on 7DMKii and 1DxMKii. I have also noticed the sluggish AF at times, but the weather has been providing a disappointingly large amount of ground fog this season.

I'm looking for the answer to the same question...

I used the Sport version for about a year and the only tweak I made was changing the stabilization to dynamic (IIRC).
I did not change the focus speed from default. The lens worked very well for birding on both 7D2 & 1DxII. I did use the dottune method to AFMA the lens on all of my bodies.
I will add that the best results (@600mm) came on a tripod w/a gimbal head.
As far as the C version goes, I got one for my wife (due to weight) and for the life of me could not get it to focus fast enough. I ended up getting her a Tamron G2 and the speed difference is day & night.
Happy Shooting!

I've been using the C version for about a year now with my Canon 80d. I found that setting the AF speed to fast and the stabilization to dynamic works better for birds in flight than the default. I also customized the focus distance to 5 meters to infinity instead of full.

I have not used my C version in awhile. Last weekend I took it to an air show and it was slow at acquiring focus. I missed several shots because of that.
While at the show I talked to photographer who had the Tamron G2. We discussed focusing speed, and he said his G2 was very fast. So now I'm thinking
of buying the G2. The stabilization in my Sigma C fails intermittently. I have to find the lens receipt and see if it's still under warranty.
Besides focusing speed, do you have an opinion on IQ between the Sigma C and your TG2 ?

Warranty in US is 3 or 4 years if I recall correctly.

Right, I checked Sigma's site and it says 4 years. That's pretty good me thinks.
Now I gotta find the sales receipt. Looked in my file cabinet and it's not there. Ugh!

One of the big advantages of buying online, log in and look up purchase history, print new invoice.

I used the C version at a couple of airshows and mine worked fine with my 7D mkII, I set up a custom minium focus distance for airshows, I can’t remember off the top of my head but I think it was something like 50’ for the minimum distance. If a plane gets closer than 50’ from me I am going to duck and not take pictures.

Of course, I should have thought of that. Just found it at BHP. I bought it in 2015 so it's still in warranty. Thanks Jake.

Thanks. I tried various settings but it still hunts a lot when acquiring initial focus. Overall it's a great lens. Just hope the stabilization can be fixed.

I am not so sure the image stabilization is working on mine either, I know I don’t trust it. My Canon lenses show a very noticeable difference in the viewfinder that I am not seeing with my Sigma.

This was one of the main discussion points when the lens first came out. The OS does not show what it is doing in the same way that the Canon lenses do. I think one of the dock settings that we all ended up using helped this. In either case, the OS did work, you just could not see it's effect as readily in the viewfinder.

The problem with my lens is this...with OS on and panning, the image in the VF will jerk about violently, and a noise or clicking sound will
come from within the lens. Any images taken at this point will be blurred. This will last for a few to perhaps dozens of frames. Then the fault
will clear for awhile but return later. Kind of a random thing. Turning off OS returns the lens to normal.
A trip to Sigma is in order.