I'm looking for information about openvpn speed on gl.inet routers, I read on the forum and on their site that maximum openvpn speed is around 10Mbps (~cheaper routers) and 25Mbps (~expensive routers). Is that a protocol limitation or a hardware limitation?
What are the openvpn speeds of MT300Nv2 and AR750S ? And the respective wireguard?
The GL-AR750S is stated to provide 17 Mbps with OpenVPN and 68 Mbps with Wireguard. It runs a QCA9563 (MIPS) SoC at 775 MHz.
VPN performance is primarily a single-threaded, compute-limited thing. Multiple cores can help keep other things from grinding to a halt on your router, but typically don't increase VPN throughput. (With deference to slh's following comment, I added the proceeding as he was typing)
I don't own any MTK-based devices, so I can't meaningfully estimate the performance. Basically, similar SoCs with similar clock speeds are going to have similar performance, from any reputable manufacturer.
Another thing to mention is that OpenVPN is inherently single threaded, so multiple cores won't speed up the tunnel speeds (but multi-core is still a very good idea, to keep the other things, WAN, routing, NAT, firewall, ethernet IP, WLAN, etc. running concurrently - basically to "offload" the more basic stuff to the other cores).
Can't speak to openvpn, but for wireguard I can confirm the numbers that GL advertises. I measured 70Mbps via wireguard on the AR750S, and 31Mbps on the MT300N-v2.