I think when it comes to 24-70's, Nikon and the third parties are in a perpetual game of leap frog now. Tamron and Sigma have always nipped at Nikon's heals with low cost alternatives. Now Tamron ups the anti with VC and a very sharp lens, giving them an "angle". Sigma's trying to carve out a niche with a 2.0, something the other two won't have. It will be up to Nikon to jump after sigma and drop the axe on them with a new pro standard. I"m sure it takes some time for Nikon to feel any sales reduction, but these two will bite into the market more vigorously than before. Nikon will still grab the majority of the FT pros, but with Fx going down in price, there's going to be a lot more buyers for third party pro alternatives. This is where Nikon may once again miss the boat if they don't respond.