Don’t spend money moving from 1G to 10G if you’re not close to saturating your 1G switch, given you’ve only got one real server then the limiting factor will be the NIC on the server and I can’t imagine an a520 Mobo with anything more than 1G. And buying a PCI NIC for it shouldn’t be a priority if it’s not strictly needed. You’re also going to be limited by your Internet speeds, the HDD speeds and a lot of other factors before you can actually really get good utilization on a 10G Port. I struggle saturating my 2.5G NIC and I run quite a bit of things and have done various benchmark tests and it’s not easy saturating even 1G with real world load. Not to mention all the new ethernet cables you’ll need since most don’t have 10G cables in their setup, but 1G capable cables are fairly standard at least.