Well I went to Tall's Cameras today and I tested out a Tamron 10-24mm and the $1.3k Nikon. The Nikon is super fast at focusing, but for the price, I would step down for the Tamron at $500. It's slow, and a little loud when focusing, but wide angles are meant for stationary objects, or set scenes, so no biggie.
So in the end I got the Tamron. The sales guy was telling me not to go with the Sigma based on its short warranty and non-existent customer service. I thought the Tamron was better anyways, as it offered a range of 10-24mm instead of 10-20mm. It has 6 years of warranty coverage, which is one more than the Nikon, so I feel pretty confident that I made the right choice.