http://www.the-digital-picture.com/R...mp=4&APIComp=0

And even at the longest it goes, inbuilt 1.4x and external 2xIII ... the corners are still better than the 70-300 non-L (although marginally worse in the centre).

now the question (which i don't have to answer until I win the lottery):
70-300L + 500/4 or 600/4 OR
70-200L + 200-400L OR
85/1.8 + 100/2.0 + 135L + 200-400L?