Sorry for bringing this thread back from the dead (I'd rather not make a new thread for the same topic).
I'm also looking into 10g networking for my upcoming NAS, especially given the dozens of TB I have to store on it. I don't see much benefit from having 2 ports, so I'm only looking at single port cards.
So far I've found the following:
Intel X540-T1 (x8 physical slot, supposedly runs at PCIe 2.0 x8 and only supports 10/1/0.1G speeds)
Marvell AQC113C (x4 physical slot, assuming it runs PCIe 3.0 x4, but have heard some mention it running PCIe 4.0 x1 and supports 10/5/2.5/1/0.1G speeds)
Intel X550-T1 (x4 physical slot, runs at PCIe 3.0 x4 and supports 10/5/2.5/1/0.1G speeds)
On the NAS side, I'm re-purposing the old PC on a Gigabyte Z97 motherboard. It has 3 physical PCIe 3.0 x16 slots, that can run at either x16/x0/x0 or x8/x8/x4 speeds (also a bunch of useless PCIe 2 x1 slots). The x8 in the first slot won't be an issue since I'll keep a GPU there for encoding (since the CPU doesn't have built-in graphics). So no problems there.
On my PC side though, I've got the Asus B650E-E in the sig. Whilst it has the same 3 physical x16 slots, they only run at x16/x0/x4 or x8/x4/x4 speeds, admittedly at faster PCIe 5.0 for the first 2 and PCIe 4.0 for the last one. Here-in lies the problem, the best I can do on this end is a x4 spare slot, since the GPU is in the first slot.
An X540 will be fine in the NAS as I can stick it in the 2nd slot running at PCIe 3.0 x8. For the the PC, ideally I need an 10g NIC that won't be hampered by only 4 PCIe lanes. Only issue is that the Intel X550 has barely any availability or even at a good price, looking like double the price of the X540. The Marvell I've heard mixed things and some say not to bother with anything other than Intel.
Is it possible to get away with an Intel X540 in the PC with only 4 PCIe 4.0 lanes? It'll still only run at PCIe 2.0 speeds... admittedly my NAS will be unlikely to saturate the 10G connection (5G would be realistic, but it doesn't look like there's much 5G options available and it's not worth it when 10GB options cost only a little more). Theoretically a PCIe 2.0 at 4 lanes does up to 2GB/s and the 10GB NIC shouldn't get above 1GB/s.
Are there any other options by now that would be reliable for only 4 PCIe 4.0 lanes?