BTW, Knock, if you're willing to settle for 2nd best, you can get up to 600mm for $700 from both Siggy and Tammy. On a crop its nearly 1,000mm eq. FOV. Insane reach for that amount of money. You have Nikon, right? I'm pretty sure both these lenses are made in Sony, Nikon, and Canon mounts.
http://www.ebay.com/itm/331720685117?item=331720685117&lgeo=1&vectorid=229466&rmvSB=true http://www.canonrumors.com/black-friday-tamron-sp-150-600mm-f5-6-3-vc-699-reg-1069/Personally, I'm going to have to pass on them. I'm leery of third party lens internals (durability of focus rings, focus motor, build quality, etc), but I'd go with the Sigma if I had to chose between the two.
