The hard limit for the RAM frequency seems to be about 2800-2900mhz on the 4770K (maybe he just lucked out), according to this guy:
https://www.youtube.com/watch?v=UH0fNDqrN0I&ab_channel=Luumi
I had all kinds of problems with my 4820K IMC wise - there was a hole around 2400MHz it didn't like at all and wouldn't go past 2600MHz - while my 1650 V2 is another kettle of fish - I've not actually found the limits of it any of the DDR3 I have taps out first - does at least 2900MHz (not really surprising as these 16xx Xeons are top tier silicon and cost thousands in their day).