Did you consider switching from OpenVPN to WireGuard? As you can see on the link you were given here, a rather budget oriented Cudy WR3000, which can be had for around $50 on Amazon (even cheaper if there's a deal), gets you to 400MBit WireGuard.
I'm not suggesting to switch to a budget router like the Cudy. I just use it as an example for how far even a budget device gets you if you're not tied to OpenVPN. As you can see in the WireGuard comparison thread, the MT6000 others suggested brings you to 85% line speed with WireGuard. You won't get that with OpenVPN.