I honestly cannot imagine anyone handholding a 500mm for more than a few random shots.
is there ANYONE on here that uses the 500mm handheld exclusively? this doesn't sound like a recipe for great shots.... and it is really expensive.
but hey, if you really want it, and you can handhold it, and no other lens works for you, i don't think it's the worst thing you could spend your money on.
The 5DIII+500mmII is a little more than 4kg. For portrait sessions, I've handheld that weight (1D series + 580EXII + glass). My backpack is often >10kg. And I'm only 1m68 and 50kg. So I guess it depends on the person.
Sure, I never enjoyed the weight. I am trying to bring less gear and work with what I bring.