What kind of stability testing did you and your friend do? Posting and booting into the OS is one thing but passing a suite of memory tests is going to be a lot harder at those speeds/timings on a Zen 1 CPU. I personally don't consider a memory overclock stable unless it passes memtest86, A long term DRAM calculator stress test, and a long term Large FFT p95 test.
Later production silicon and newer BIOS versions probably help getting better memory speeds/timings so I guess it's possible things have improved in the 2 years since I've played with these chips. Not to mention silicon lottery and mobo memory topology/trace layout are pretty major variables. I still think getting anything 24/7 stable above 3200 with good timings is atypical on these CPU's. Early on many people were struggling to even reach 3200.
I'm not sure if you are still disputing my CPU clock/voltage observations but FYI they are completely in line with Silicon Lottery's historical binning statistics.
Historical binning statistics from Silicon Lottery
siliconlottery.com