Keep Sigma 10-20 or upgrade to Tokina 11-16?

I have had my Sigma 10-20 4-5.6 for more than a year. I love the lens, mostly use it on the 10mm end. I mostly take pictures outdoors, but sometimes indoors with bounced flash.

I found a 11-16 locally and I am considering the switch. Going with the Tokina, I lose HSM and 10/17-20mm, but gain f/2.8.

Has anyone made the switch? Is the Tokina sharper? or just faster? How's the focusing compared to HSM or USM. Based on one youtube video, it's very quiet compared to the kit lens or Sig 17-70.

Advice?

It's out of stock... Aging...

Stock is not an issue, it's for sale locally.

Do you find yourself shooting in low light conditions often? Do you use a tripod for those shots, if you do?

Really depends on what type of shooting you'll be doing.

If the price is good... buy it. Worst case scenario you re-sell it at a profit =)