I own a 500 f4 USM IS (not II). It is an outstanding lens for wildlife but it is big and heavy. I've seen people hand-hold it but I don't think you are able to take full advantage of the resolution of that lens doing it. You'd need a sturdy tripod and ball head or Wimberley type mount. If you're flying, it might fit in the overhead in its case by itself.
The IQ however, is much better than the 100-400 or the 70-200 with a 2x teleconverter.
I will be driving, and have a manfrotto 055xpro (8kg) tripod which i think should be ok...
Thanks for the advice, i'll let you all know what happens, and photos of course... I'm hoping for some big cat action!