Yes. PCIe 2.0 has 5 gigatransfers/s per lane, so here 4x5 GT/s. Subtract approx. 20% for the encoding, which leaves approx. 16 gigabit/s.

By the way, I can't recommend the card very much, because it has pretty bad driver support (no matter if Windows or Linux).

With the Intel card, everything worked right away (Linux; Ubuntu) or by installing the drivers (Windows).

Intel X540-T1: 10Gbps Server Network Card

As already mentioned by the previous speakers, PCIe 2.0/2.1 x4 achieves a whole 2.0 x 10^9 bytes / s (https://de.wikipedia.org/wiki...), i.e. around 2GB/s, depending on whether you calculate with 1000 or 1024 bytes. 10Gbit corresponds to a theoretical 1.25GB/s. This is sufficient for the PCIe standard alone. I can't say yet how stable the card is at 10Gbit or 5Gbit 2.5Gbit, because it is currently running at 2.5Gbit and has only been for a few days. You have to be more careful with the connection of the data carriers. For example, if they are connected via SATAII (3.0Gbit/s) or SATAIII (6.0Gbit/s) (and not directly in the PCIe), 10Gbit on the network card will only be useful if the data carriers are connected in a RAID or if data is read or written from different data carriers in parallel. I also assume that you have the necessary routers / switches and the corresponding cables for 10Gbit. But I assume that all this is clear to you. Sometimes, however, you see that some people do not realise, for example, that a 10Gbit Swisscom Internet line via the Internet Box 3 on the 2.5Gbit port cannot deliver 10Gbit to a computer with a 10Gbit network card. They then ask themselves why the computer only receives 2.5Gbit and do not understand that the bottleneck is the 2.5Gbit port of the Internet Box 3 and not the 10Gbit network card in the computer. ;-)

PCIe 2.0/2.1 has 5GT/s and the maximum data rate is 2,000 GB/s with PCIe x4.
Nevertheless, I consider the stability of this card to be poor.
It has no place in servers and NAS (it really annoyed me and I switched to Intel).
Only in a desktop PC will it make some sense.

Speed-wise, it shouldn't be a problem. Maybe it's an older card that doesn't have all the enterprise features, but if you just want a fast connection, it shouldn't be a problem.