Weird, my rev e does 621 at 4137 with trefi maxed. Getting slightly higher bandwidth than yours at 4137 cl17. Identical latency.This higher tRFC is standard for Micron B-die; it's really only Samsung B-die that can push much lower. See chart below.
My PC will intermittently freeze if I attempt even 650. I could test down to 660 or so, but I don't really feel like squeezing every little bit out of it.
View attachment 2466468