I don't know what the world record is, but I may have seen it on Xray. Back when I was working in a cath lab that also did radiology cases, we had a case in there with stones that literally filled the entire calyces on the back or the kidneys. The stones were close to the same size as the kidneys. Our job was to put stents from the calyces to the bladder to stabilize her till she could bet surgery for the removal. I doubt those two caused any pain by being there, but she may have already passed pieces and other stones.
WA