Experience with the Sigma 120-300 Sport shooting sports?

I shoot a lot of sports, and I currently use the EF 70-200/2.8 IS II indoors and the 100-400L for field sports.

I was thinking about updating the 100-400 to the new version, but lurking out there is the Sigma 120-300/2.8 Sport. There are times I could use 300mm and f/2.8 inside, and the idea of a 168-420/4 lens for fields (using a 1.4X TC) is really appealing. It's essentially the range of the 100-400 but a stop faster.

But the wildcard is AF performance. Faster is better only if the shots are in focus. Anybody have experience with this lens on bodies like the 1D4 and 5D3? Can it do the job for sports?

And what TCs does it like? I have the Canon 1.4X II, but I could use a different one if it would make a difference. I'd love to hear experiences with this lens on demanding AF subjects.

Jeffrey,
I have the non-Sport OS version, a very sharp copy. I have not shot any sports with it though, only wildlife.
I found the tracking to be quite good, even with the 1.4x TC. I'm sure a Canon 300 2.8 II would track even better but my keeper rate is very good.

As for TC, I can tell you that my Sigma works best with Sigma APO EX DG teleconverters. First I had a Kenko Pro 300 DG 1.4x, which I thought was pretty good (it's generally well-liked). Then I thought I'd give Sigma's 1.4x a try. It is significantly better, sharper, better contrast. So I stayed with the Sigma.
As for 2x TC, I had about 4 different ones, including 2 (!) copies of Canon 2x III. My Sigma 2x beat all of the other competitors in sharpness. The Canon 2x III had better CA control, and was a tiny tiny bit larger in magnification. But again I stayed with the Sigma since it was the sharpest 2x I've tried. (I had 2 other ones, cheaper ones that were inferior to both the Sigma and the Canon.)

The 120-300 OS + 1.4x TC is super sharp on my 5D3 and very sharp on my 70D. Even the 600mm 2x Sigma TC shots are nice and sharp on my 5D3.
But like I said, I've never shot sports. Once I tested my 6D's tracking AF on some runners in the park, and it worked great, even with the supposedly "unusable" off-center points (that was actually the purpose of my test back then; to prove that under descent conditions, those off-center 6D points were actually more usable than most people think.)

Here are some examples of the 2x Sigma TC, 600mm, on the 5D3. These are 100% crops. Wide open, then f/6.3

IMAGE LINK: https://flic.kr/p/oR5Y​3h

IMAGE LINK: https://flic.kr/p/pMGM​MD

I have the non sport OS model on my 5D3 and this lens is rock solid. I only use lens that produce reliability and this lens is it for me.

My buddy has the same one that me and Gabe has also and he has a 1dx, 1d4, 7d2, 5d3 and just sold his 6D and they all worked great with the 120-300 OS non sport.

No experience with the sport model although I do want to upgrade for no reason other than I can.

I have the Sports version - for about 5 months. I debated on a used Canon 300 or the Sigma and the Sigma won because I was losing the whole center ice when I borrowed a 300. It does not focus quite as quickly as the 300, but it's damn good. My boss borrowed it for a hockey tournament and agreed with me - very good but not quite as good. I like the zoom ability. I've been happy with its performance

Thanks for the responses so far, I'd love to hear more.

Ironically it was the release of the 100-400 II that got me started thinking about this lens. I initially was thinking maybe to upgrade my V1 of the 100-400 for snappier AF and better IS performance. But I've always been intrigued by the 120-300 due to the combination of range and speed not available in any other zoom. I'm seriously thinking about it.....if I can get the 120-300 bare working happy inside and then with the 1.4X TC for field sports I'd be happy over the older lens.

Then the question is, do I keep the old 100-400 as my 'lightweight' travel long telephoto?

Well, first step might be to give the big Sigma a try and see how it does. I can shoot some indoor soccer and stuff this winter with one and see what I think I guess. If it can handle that, it should work well.

i use mine on my 70D for my nephews soccer...i'm not sure what level of sports you're planning on shooting, so none of this may apply, and i'm not using the bodies you were after...it does track well, i'm not going to lie though, i do stop it down to f3.2, because i felt like shooting at f2.8 I was missing a few shots because of the DOF...I have a feeling that the large majority of missed shots are me, and not the lens though...still not positive about my custom functions for AF on the 70D for sports...not sure if i should put the AF on the lens to fast, or accurate...I just haven't had too much experience shooting sports to say for sure when i miss it's the lens at fault

i do find it harder than tracking BIF, but i've also done a lot more of that than sports....another reason i'm not happy with some of my shots is all just down to the lighting...shooting at high noon is not something i'm used to when it comes to processing, so that's been a bit of a learning curve

actually not sure if this post helps you at all