Sigma has announced they're going to challenge Tamron in the 150-600 zoom range prior to Photokina. It seems they're aiming at a higher end market with this lens for those of us unable to make the huge step up to the more exotic 200-400 type zooms or their 120-300.
http://petapixel.com/2014/09/05/sigm...-3-sport-zoom/