I managed to buy an IS-60 on ebay, but it sure looks like it's out of production. I had to sell it though, clearance issues with my Asus B360i motherboard.
I have done one run of Cinebench R23 test with both the L9a and the 47K in an open air bench , assuming stock 5600X without PBO, the temperature difference is 3C, both with the same NF-A9x14. I would think in an enclosed case environment, the 47K will probably be better by a couple more C, but not much.
Edit: No backplate used for both, because my motherboard is a MSI B550I, which has components at the back, which disallows the use of any backplate unless it's the stock one that comes with the board. (Screw you MSI).