True, that could work.... you don't mention the 100-400 here Tony... any reason?
I guess they are all L lenses so how bad could they be surely? Or am I wrong?!?
100-400's are a bit of a mixed bunch by all accounts, I don't think there's anything wrong with my one, but Tony thought it was a bit soft (he was comparing with primes really so no suprise there)
In terms of 70-200 f/2.8 IS plus TC's and comparison with 100-400 (I've got both) I'd say the 70-200 with a 1.4x TC is every bit as good as the 100-400 on it's own so unless you need the 300-400mm range you can easily get by with a 70-200 + 1.4x TC.
I've heard that the 2x TC makes the IQ on the 70-200 a bit lower in quality than the 100-400 but haven't tried it myself...