Body advice for a prime lens.(wildlife)

Hey all, i recently found a good deal on a 500mm f4 IS and am now looking to get a body for it.

I had a d800 with a 200-400 VRII, but sold the 200-400, will be replacing it with a 200 f2, and use canon for the long distance shooting.
The canon will be on the 500, with or without the 1.4 converter.

I have been reading up a lot on canon , but am not quite sure yet.

The options that are out there are the 1d mkIV / 5d III , or maybe wait a few months and see if the 7d gets updated.

Autofocus is important, and opinions differ on that subject, some say the AF for tracking is better on the 1d, others say the 5d III is better., 10fps is nice, but i come from 4 , so 6 is already an improvement.

What kind of advice/or thoughts do you guys have ?, or maybe any first hand experience with a 1d / 5dIII and the 500mm IS, it is the IS version and not IS II.

There are some nice second hand 1d Mkiv's for around 3k$ ( which is around the price for a new 5dIII), so they are similar in price.

Thanks in advance for the advice.