Tamron 28-75 vs Tokina 28-70/80

I am looking to purchase a midrange zoom that will be used in low light with a Nikon D7000.  I am looking primarily at using them at F2.8. I am currently debating on a few different lenses

1) Sigma 17-50/2.8

2) Tamron 28-75/2.8

3) Tokina 28-70/2.6-2.8 or /2.8 (2 versions looks like are available)

4) Tokina 28-80/2.8

I have dont alot of research on the Sigma and Tamron, but havent really found much good info on the Tokina's.  Does anyone know how well they operate at 2.8?

I understand the difference in focal ranges and I do think I would miss the 17-28 mm difference.  However, I also own the 24/2.8 AI and use it occasionally when needed and would put the money saved between the Sigma and the others towards a wider angle lens.  Also, I feel that 28mm is plenty wide most of the time and would like the little extra reach at the wide end to help reduce lens swaps.

Other lenses owned that are used for this style are the 35/1.8g and 85/1.4 (rokinon).

Thanks