As soon as you say "BIF", the 400f5.6 should really be first in line.Thank you. That seems to be the conclusion I'm reaching myself as well.
The 400f5.6 is also very light for what you get. Basically you cannot do better if straight "BIF" is what you are after.
That lens is such a special piece that the lack of an equivalent in any other mount is the primary reason my gear set is Canon exclusive.
I almost want to get another and glue a TC onto it (which should theoretically produce a completely weathersealed lens), but fingers crossed the (rumored) 100-400 upgrade will be something spectacular, and we have the SX50HS successor to check into for super(ultra)telephoto options.