Canon has officially announced the new 200-400mm f4L IS lens with a built in 1.4x extender and already there is a five page review with Dxomark test results included published at Le Monde de la Photo. Here it is, page #1 and page #2 and page #3 and page #4 and page #5.
The lens is available for pre-order for $12,000 at Adorama.