Killer E2500 LAN issue

Hi, I have a mobo Gigabyte Z270 Gaming k3 with Killer E2500 LAN chip, I installed some kext but the network card is not working properly, ie: in a speedtest I can't get full speed. I got half more or less...

Somebody could tell me where to found the appropriate kext for this nic?

Thanks.
Edit: the current kext I've installed is: AtherosE2200Ethernet.kext