Just a suggestion for another review (like you haven't got enough work to do Gordon

)
I know that one of the lenses looked at by many many animal enthousiasts as a relatively cheap alternative is the Sigma 150-500. Unfortunately it's very hard to find a reliable review of this lens, as they seem to contradict each other quite often.
I for one would really like to find out whether this lens performs the way we all want it to, because it costs about 2/3 of the canon 100-400 and gives a nice little extra reach. This one might have to be tested on different bodies which could make it hard, but I'm sure a lot of people are wondering whether to get this one or not.
Regards,
Paul