until something better comes along the tamron is the way to go.
tamron vs 400 5.6L
tamron vs 70-200ii plus 2xiii at 400
those crops show the tamron and the 400L look about the same at 400, the tamron is a 150-600 zoom has vc, cost less, and has a 6 yr warranty.
the tamron looks better at 400 than the 70-200 plus converter at 400
pretty much everything i have read from people that have or have used the tamron are pleased with it
I compared the Tamron at 400 against the 70-200 and 2X teleconverter.... no comparison, Tamron wins.
At 200mm with no teleconverter, no comparison, Canon wins.
AF is definitly faster on the bare 70-200, but is comparable when the teleconverter is in play.
Good luck finding a copy of the Tamron... there are long waits to get one. This should be telling you something