I just go for Samsung ECC memory, ECC is also helping to reduce the risk of memory-related crashes due to too high frequencies even if it is counter-intuitive…
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8 GB/module: Samsung DIMM 16GB, DDR4-2666, CL19-19-19, ECC (M391A2K43BB1-CTD)
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16 GB/module: Samsung DIMM 8GB, DDR4-2666, CL19-19-19, ECC (M391A1K43BB2-CTD)
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32 GB/module: Samsung DIMM 32GB, DDR4-2666, CL19-19-19, ECC (M391A4G43MB1-CTD)
Just give them 1.35 V, make sure there is a little air flow over them and clock them away. Anything above DDR4-3800 is more or less just for dick/vulva measuring, get the timings as tight as possible and keep IF clock 1:1 to memory frequency (1900 MHz for DDR4-3800, for example).