im not on 10gb(or your ISP, im in the USA), but I have tested it LAN to WAN with a firewall, and was able to get just over 8gbps sustained on an e3-1220, I have since upgraded to an e3-1270v2 and have never tested it since, but I would assume its a bit faster due to higher clock speeds.

The cons is the space that required, but I can move it on the garage/basement.

Its a 1U rackmount server, so having a vertical wall/rack mount system like this is what I have given as an option before. Keeps it flat against the wall, so minimal space needed, really.

Do you know the power consumption?

mine idles right around 20w to 25w with the 10gb card in it, and on a 1gb transfer it still sits just above that idle number at around 35w. It will sit idle most of the time. I have never seen it hit more than 50w on anything, and that was likely because the fans had ramped up. noise is an issue with these, they aren’t quiet unless you keep the room cold, so if you can put it somewhere where you don’t have to sit next to it, or within a few meters of it, you should be fine.

Don’t know how expensive power or used servers are in Italy, but I personally run a Dell R210ii server that I bought used with a dual port 10gb NIC. In testing, I was able to get around 8gbps with no tuning on PFsense. There are no consumer or prosumer routers that can actually hand 10gb NAT/firewall without stepping into really expensive commercial stuff that just isn’t worth it for the home.

your modem’s access address is 192.168.100.1 it will not have a subnet in bridge mode.

Who takes the effort to remove the mounting rails? Take it as a lesson learned for next time, and find a server rack with actual square hole or round hole mounting rails.