Upgarade 100-400, or try 120-300 Sport?

When the 100-400 II was announced, I was thinking to upgrade my current 100-400 which I use for a bunch of stuff + field sports. I like my current 100-400L quite well, but I'd like better IS and the expectation of IQ on par with my 70-200/2.8 IS II.

I use my 70-200/2.8 IS II for a lot of things, including indoor sports. I use the 100-400L for a lot of things, including field sports in good light.

One alternate thought I had was to instead pick up the Sigma 120-300/2.8 Sport. I could use this for some indoor sports...and also add a 1.4X TC and use it for field sports with one stop better than the 100-400.

What is the general take on the 120-300 Sport for indoor sports in low light, and again on the field with the 1.4X TC? How does it stack up for focus performance?

That is my biggest concern, ability to acquire and track targets, as that is more important to me than most anything else. I'm especially interested in how well it works with the 1.4X TC as a 168-420/4 field sports lens.

Indoors I'd like it for volleyball back through the net. Anyone use it for this?

Where did you land on this decision and how did it work out for you?

I can't justify the expense of the 120-300 S for what I do. I can tell you that when I am shooting my 100-400 I am wanting for aperture a lot more often than focal length.

mmrn59 wrote in post #17784476
Where did you land on this decision and how did it work out for you?

I wound up getting the 120-300 Sport. I also still have my 100-400L and I have my 70-200/2.8 IS II.

I still tend to use the 70-200 the most for indoor sports. I use the 120-300 a bit, typically when I need the reach to 300.

For outdoors, often the decision comes down to portability and how badly I think I'll need the speed of the 120-300.

Overall the 120-300 is an excellent performer. It is great optically, and it works very well with my 1.4X TC. There are a lot of situations where the speed and isolation I can get with this lens are perfect.

That said, the AF performance is good but not as great as I can get with my Canon telephotos. I trust it on moving subjects, but the keeper rate falls off when I push the lens hard on very fast and erratic subjects.

Example, my second daughter was in a band this year, the lens was just ideal for that. She also played indoor soccer last winter and the lens was pretty good for that.

I also shot my oldest daughter in diving and volleyball, I would say the lens struggles with those topics due to the erratic motion. I might have some examples of that, but for now I'll stick in a couple from the first two things that this lens does very well.