@neuroanatomist - yes, renting a 300/2.8L and a 2X extender would definitely give me massive reach. However, that's a heavy lens, so I would definitely be leaving a lot of other gear behind in order to make room (no 70-200 for sure, and any thoughts I had of sneaking a wide-angle lens into my wife's baggage would probably go by the wayside as well).

Question is, how much value would I get out of it? Is that combo mostly useful for birds (which I'm not that bothered about), or is it considered essential even for larger game?