I have finally purchased the Zeiss Distagon T* 15mm f/2.8 and will be putting it through paces on a two week trip to Namibia beginning on April 6. For filters, I'll be using the Sigma 95mm DG Circular Polarizer, as well as large Singh-Ray grads when needed.
My immediate first impressions are quite good, amazing build quality, great zoom ring and the silly test shots looks terrific. I'll be shooting exclusively with the EOS 6D on this trip.
Justin has received the Sigma 120-300 f/2.8 DG OS for review and he'll be putting it through the paces with the EOS-1D X. He's already shocked at the size and weight of the lens. No, it's not a “hand holding” lens for most people. The first 2 negatives you can give the lens is the heavy and unnecessary metal lens hood and the equally enormous tripod foot. Third party accessory makers could surely knock a pound off the lens replacing both parts with lighter weight materials.
Optically and AF wise the lens is very good with initial test shots, Justin has the USB dock and will also put that through its paces.
Both reviews should be online some time in April, though I'll be posting images from the Zeiss 15mm as the trip progresses.