Slow internet speed using PPPoE on Netgear R6800

I have problem with internet speeds using PPPoE. Before I was using DHCP client and I had around 800mbps, but when changed internet provider I had to use PPPoE and I have speeds max at 350mbps. When I connect my cable directly to the PC with set up PPPoE I have ~700mbps. On OpenWRT with maxed out speed at around 350mbps I have very high cpu usage. Is it realted to drivers? and if so, how to install them. Netgear R6800

PPPoE isn't the lightest protocol, and the R6800 has a (by modern standards) relatively weak MIPS SoC. How is CPU load looking when you're doing 350 Mbps?

I have around 90% cpu usage on all cores