Suggestion for a 2,5Gbe PCIe x1/x4 (or 10Gbe?)

Hi everybody! For my OPNsense router (on a VM on Proxmox) I need a 2,5Gbe card (to connect to the ONT of my provider); I only have 2 PCIe 3.0 x1 or 1 x4 because the only x16 is for a dual SFP+ fiber card.

Can you suggest me a NIC (I'd prefer to buy used)? Is it better to go with a 2,5 or 10Gbe? The cooler (temperature!) the better. I just need 1 port, if there are 2 it would be better, but the most important thing is the low operating temperature.

Thanks!