I am just an interested bystander at this point. My 100-400L does not see much, if any, use in the winter (just zoo trips if we have a break in the weather, and 400mm is enough there), so there is no need for me to buy anything now. I can wait for more reviews, and a possible Tamron rebate, before deciding on anything. Besides, I hate the idea of giving up the 100-400L due to the size and weight difference -- and my copy performs very well. I pack the 100-400L a lot when we fly, and it's very compact for a long telephoto zoom lens.