Very impressive performance by the Sigma, particularly with the T-Stop. I recently weighed this lens vs. the Canon 300mm f/2.8L IS II and ended up buying the Canon. I already had the Canon 70-200 f/2.8 IS II and both teleconverters. I found the flexibility to go from 300 to 420 and 600mm while retaining most of the image quality a better fit for my needs than the ability to zoom from 120-300mm. Others have different needs, but I thought I would share my tie breaker.