Do you have access to a WireGuard VGPN endpoint, or are able to configure one on a VPS yourself (~US$5/mo)?
Based on GL.iNet numbers, so at least self-consistent
- ipq40xx (717 MHz) -- 192 Mbps WireGuard -- 25 Mbps OpenVPN
- ath79 (775 MHZ) -- 68 Mbps WireGuard -- 17 Mbps OpenVPN
As you can see, the load of OpenVPN at even moderate rates exceeds what a MIPS-based router can handle.
To get 50-100 Mbps over OpenVPN, you're likely looking at an x86_64/AMD64 solution, with a separate all-in-one as an AP.
Based on that, I'd recommend an ipq40xx-based unit, or one of the faster SoC families, such as ipq80xx, mvebu, or x86_64/AMD64. I don't have experience with the mvebu wireless, but I find the wireless performance of the ipq4019-based EA8300 to be noticeably better than that of the ath79-based Archer C7v2 units I've replaced. Recently someone here posted that Amazon UK had EA6350 dirt cheap (£34).
Ignore the title, but this post has some good starting points: