A YouTuber has already managed to buy a retail unit of the unannounced Intel Core i5-12400 CPU. Upon benchmarking, the Cinebench score of the retail Core i5-12400 came out slightly lower than the Core 15-12600K. As for temps, with only the stock cooler, the chip shot up to 81°C (177.8°F).
https://www.notebookcheck.net/Retail-unit-of-the-unannounced-12th-gen-Intel-Core-i5-12400-impresses-with-strong-performance-and-manageable-temps-with-the-stock-cooler.589455.0.html