If you have the spare cash, I think you should keep the 12-50 until you have the 25/1.4, cos the latter can be hard to find and you'll be without a lens in the meantime if you sell the former first. Better still, keep until the 12-35/2.8 is released. You never know what kind of delays can happen with a new lens launch, and the price might scare you off. (Rumors say upper US$1000s!)