The router is already up to the job - it has a 2.5G WAN port and one 2.5G LAN port. I bought and installed a 5-port 2.5G switch and a long superfast patch cable to link the router to the switch. These things aren't the issue. It's the end equipment (PCs and so on) which are all limited to less than 1 Gbps.
I'm not going to lose any sleep over it. The system is more than fast enough for my needs and I'm not going to waste my life away nitpicking over unimportant speed issues.