Perhaps...no, definitely not the hardest we have seen in terms of numbers, but this video by Derek Thatcher of James Morris on Weapon Omega at Flock Hill, one of New Zealand's hardest at 8A+, certainly gets a good score from me.

If my information is reasonably correct, you'd have to be a master of manteling to get to the top of anything at Flock or Castle Hill and I think this video illustrates this quite well...

Source: Powerband