I tried it [FTTP, supposedly gigabit], and had to stop using OpenVPN because of disappointing performance.
Various resources such as this
led me to believe 500mbps - 800mbps should be possible if AES-NI were active on both endpoints and if we could adjust MTU.
I saw no better than ~230Mbps, and the load on my appliance led me to believe the Sonic endpoint was the limiting factor.
It was great for FTTN, but off by binary orders of magnitude for FTTP.
In other news, off VPN, I'm seeing less than 700Mbps down, highly dependent on time of day, sometimes <600 but consistently >900Mbps up, leading me to believe AT&T is under-provisioned somewhere along the path.