Chewy, if that post above was supposed to talk Dave out of buying a 1D-X, it failed. Hell, I'm ready to get one now.
I have a question with regards to super-teles. I was daydreaming the other day and looking at a 400mm f2.8 IS II. Using a 2x TC would give you 800mm @ f5.6 with IS, which seems very attractive. What are your reasons for going with the 500 f4 IS over the 400 f2.8? Wouldn't the speed of f5.6 vs f8 be useful? Or does the added reach outweigh that?