Since Wireguard uses encryption, it's limited to the maximum throughout of the CPU. For OpenVPN it's around 30 MBPS (with the CPU overclocked such as in my build) and there is no way to overcome the issue beside from using a more powerful CPU to handover the job (for example, a Raspberry Pi).
Basically, you are pushing the CPU to it's limits and your results are consistent with the results observed for OpenVPN.
If you want more performance, handover the job to a 64 bit Raspberry or to an x86 mini laptop or a unused PC.