Juraj, so you have RJ45 cards and cabling, not SFP+?
Yes, so I could keep everything compatible and hassle free. Copper cabling is no-brainer. I use Intel X520-T2 cards (OEM, buy them in bulk from China), CAT6A STP( shielded ) cabling, and Netgear XS708E v2 switch.
SFP+ cards are incredibly cheap to get (even for as low as 10 euro each hah !), but the switches are problematic as SFP+ optic is mostly meant as switch-to-switch connection only, so you will find corporate switches like 40x1gbit RJ45 + 4x10gbit SFP+ which is far less useful than having 8-16 10gbit RJ45.
Then, some people go for optic because it's easy to connect two computers directly these way.
Few notes: It's not often stated, but you can even use CAT5A cabling for 10gbit, although CAT6 and CAT6A (CAT7 is just side-grade to improve audio quality, not an actual new version, ignore it) will hold up better over longer lengths.
There is third option for affordable 10gbit network, Infiniband. I strongly suggest to ignore it.