What is the probability of finding a block with a capacity of 5-6 Th? There have been cases?
Assuming no difficulty change:
On average ~ 1 block every 4.8-5.6 years. (could be 1 block today and nothing for 5 years, 1 block every 5 years, 5 blocks this week and nothing for 20 years, or 5 blocks 20 years from now - it all depends on luck)
It's been done with less.