What is the world's hardest jigsaw??

This could be debated of course, and I am sure we have all met our match with jigsaws that have stretched our patience, but many experts consider the most difficult to be 1965 Springbok Puzzle

“Convergence,” based on Jackson Pollock’s painting of the same name. I can't say I am in any hurry to try this one! What is the hardest jigsaw you have tried - tell us about the one that has challenged you the most, we'd love to hear from you.