The increases size, weight, and cost simply don't match the 1/2 stop gain. (speaking of the 85 in particular.) Not even close, IMO. Different filter sizes as well. Since the lens already has some corner-softness (wide open) issues, severe longitudinal CA issues, and is pretty prone to ghosting/flare, I just can't see how f1.2 helps any of that, at least not at a size, weight, and price I want to pay.