Warning about RealTek adapters - again!

[Bob.Dig]

they will prefer PCIe 4.0 x1 over PCIe 3.0 x2 (they can do both)

Don't think so, I bet the x4-card will only do PCIe3. But if you had no luck till now, it will not change with these.

[Stormscape]

I've seen the 8127ATF SFP+ NICs and I wonder if they work any better than the 4.0 1x BaseT cards. I've also noticed they're all 4x, so they're presumably PCIe 3.0 only. If they are, putting them in a 1x slot wouldn't get a full 10 gigabits, but it would still be 7.5 gigabits which ehhh... close enough.

[meyergru]

I think that is a misconception. Realtek advertises those AT variants as being either PCIe 4.0 x1 or PCIe 3.0 x2, but that is only to show its capability to support the full needed bandwitdh with PCIe 3.0 mainboards (provided that they have at least 2 free lanes).

Matter-of-fact, the cards will train at the highest speed they can find. That is just how PCIe works.

So, if you put them into a PCIe 4.0-capable system, they will use PCIe 4.0 x1, regardless. he only only you have on a PCIe 4.0-capable system is to limit the slot to PCIe 3.0 only. Givingg the card more lanes is not gonna cut it.

As it turns out, these Realtek adapters are on the edge of the PCIe 4.0 specification and the X570 chipset is known to be finicky as well. You may have better luck with other mainboard chipsets.