Appreciate the input.
The more I think about it, seems I would probably be best served by keeping and using the Canon 100-400 and enlarge/crop if necessary.
Hey Bob,
Did you ever get the Osa Mauser?
As far as AF goes with a 1.4x TC you may want to research that as some of the aftermarket TC's like the Kenko or Tammy may not report and so your AF will work. You can also tape the left three pins so your your 100-400 will AF with the 1.4x. I have done this with the 100-400 several times. However this is something you want to test with your lens in advance as the AF can be slower.
Instead of just focusing on FL I'd suggest you give aperture some thought as well. The 100-400 is already f5.6 @ 400mm and you loose another stop with the TC.
You may want to consider looking for a used Canon 300 f2.8. You could use it then re-sell it after your trip and have use of the lens for little more than the cost of freight. This is far more cost effective than renting if the purchase is an option. This way you would have 300 2.8 and 420 f4IS with the TC at a fraction of the cost of the 500 f4IS.
Either way the 100-400L is a great piece of glass for your trip that offers a lot of flexibility.
http://www.dgrin.com/showthread.php?t=29503
