If you are able to find a used Netgear R7800 (X4S Nighthawk) at a reasonable price (new ones are pricey), that is pretty universally agreed in the dd-wrt forums these days to be the least troublesome router with solid speed for use with dd-wrt. Supposedly it runs OpenVPN at around 100 Mbps, and there are flashing instructions in the forum at https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=320614. The AirVPN setup how-to is at https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=321856, though note it has not been updated yet for OpenVPN 2.5. Find general dd-wrt OpenVPN guidance, including notes on changes needed for OpenVPN 2.5, at https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=327398. You'll need to register as a forum user and be logged in to download the pdfs. The forum that discusses the R7800 and related routers is at https://forum.dd-wrt.com/phpBB2/viewforum.php?f=28, and it's important to check the new-build thread there for any build you are considering flashing, just to make sure R7800 owners are not having trouble with it. There is a dd-wrt router database that is referenced in a million online how-to articles outside the dd-wrt forums. Ignore it. Its build recommendations are poor, sometimes disastrously so. Usually the latest build is the right one for that router.
Re solutions other than dd-wrt, I do know that those Asus routers running AsusWRT offer OpenVPN, though they use Broadcom wifi hardware rather than the generally preferred Atheros wifi hardware. If you go that way, pick a model that is supported by (with many users) AsusWRT-Merlin (see https://www.asuswrt-merlin.net/), so that you will have the option of eventually upgrading your firmware to it. AsusWRT-Merlin is much less aggressive than dd-wrt with adding exotic features. It fixes bugs in the original AsusWRT and extends router capabilities in certain areas in a relatively gentle way. I believe I remember that OpenVPN Policy Based Routing (routing some but not all clients through the VPN) is one of its additional features. You'll either want PBR or two routers, one for VPN and one for bypassing it, in any practical router-VPN setup.
I know little about other options so will let others comment. Good luck.