From what I've seen these lenses usually have to make their way into the hands of the public to start to see things like BIF shots or motorcycle races. Even the typical lens review sites (Bryan is an exception) have shots of statues, building facades and outdoor cafes.

I'm really interested in the Sport, but even more interested in the Contemporary. If the C does weigh less (a lot less), and is optically close with decent AF performance it's a cinch. I find it odd though that Sigma doesn't know the physical specs of the C lens, you would think of all things that would be pretty much written in stone at this point? Anyway, I don't tend to shoot fast moving objects, so the C could be my cup of tea. Of course, it could be that once I have a lens like this I might change my mind! I've never used anything like this so I'm not sure just what will happen. I'll certainly be going to Elkhorn slough - a nearby and well known sanctuary for birds and wildlife. While I like the (assumed) cost savings of the C, the S really isn't that much more for its potential. Anyway, I have a Tokina 500mm reflex that I never really used for my Nikon DSLR's, so this is really going to be a new thing for me.

Sadly, my Tamron 150-600 arrives tomorrow!
Did you ever think you'd hear somebody say that? I was going to cancel my order when the Sigmas were announced, by I got distracted and after almost 3 months, all of a sudden I got my congratulations email from B&H! Although I'll test it out, I'm 99% sure I'm going to send it back. Even if the AF and IQ performance were identical, the advantages the Sigmas have (sealing, optic coatings, USB dock, new TC's...) outweigh the Tamron considerably IMHO. Plus, I've had fantastic luck with my Sigmas and love them all, and Tamron - not so much.

Anyway, I may be kicking myself for letting go of a bird in the hand for something unknown moving around in the bush. And of course, I might not have the Sigma until this summer if I'm lucky!