I'll also look to take Condyk advise and see if I can pick up another camera. Maybe upgrade mine to the 6d and sell the 60d
/QUOTE]
Even buying a 3-4 year old body that's well rated is a good move. One of the small ones. You can shop around for ages and bag a bargain for £200 or so, then sell for the same or more when you get back. I have used the 1D mkII N a couple of times, bought a decent example and immediately sold on my return. On my last trip I actually liked it so much it was used more than the main body.
Does the 60D AF at F8? I'm thinking 100/400 (f4.5/5.6) or 400 F5.6 plus a 1.4 converter for maximum flexibility, my first choice would be the zoom. I have both and having the ability to frame with the zoom, plus IS, makes it a better all round lens, if you're pixel peeping the prime might be just a bit better, but, will you be pixel peeping? All boils down to if the 60D will af with the lens and converter, otherwise I'd be tempted to go with a longer single lens. 400 f4 sounds expensive/heavy, how are you going to transport it in the plane?
Matt
The 400mm 5.6 is Ok with a tcon but you won't AF with a consumer body. It's not ideal unless the light really is A1, so restricted times of day. I wouldn't use it as a matter of course, just for the exceptional moments when you really need it. The 400mm is mainly great as most of the time you will be (should be!) on a bean bag or monopod, depending on your vehicle set up. This makes the IS advantage a bit moot, but obviously it can be a good to have now and again. Framing wise you either shoot with the prime knowing you'll crap as needed later, or with the zoom the cropping is 'built in'. I wouldn't use the tcon with the zoom. You will get a decent shot now and again but you'll likely find your keeper ratio is quite poor what with trying to MF at long range with all the dust and haze. Maybe another reason to consider an 1D MK II N?