Ah, thanks, I hoped that somewho else tries it OK, it seems to be indeed a memtest86+ problem then - see also the strange frequency and CL-values. They seem to be random, and after a short Windows boot there are zero.
On one of the laptops I got one bit flip with 4x memtester 1536M, but during a nigh-tlong test no further problems.
For people hunting PC7 in linux. There is an alternative driver for realtek ethernet card which is way less buggy then one from realtek https://github.com/KastB/r8169.