You need to understand that Wireguard is computationally intensive. There’s a dataset of Wireguard performance tests on this forum:
Take a look and see what kind of hardware matches your future performance expectations.
Generally speaking, Wireguard performance depends on the processor’s capabilities (speed, number of cores, optimizations) and cooling.
As to specific devices, I have to declare my bias: I LOVE OpenWrt on x64. Some affordable (if bought used) x64 devices, in addition to what @frollic has recommended, are:
- AppNeta m35 (it’s a rebranded Lanner FW-7525, as is CloudGenix ION 2000 recommended by @frollic)
- Star2Star StarBox 2500 (another rebranded FW-7525)
- The original FW-7525 sold under Lanner brand is occasionally seen in the wild as well
- Lanner FW-7551 rebranded for Silver Peak (this one used to be unworkable, but recently, BIOS passwords for it were extracted, so now it’s completely tame)
- Sophos 85 / 86 / 105 / 106 / 115 / 125 / 135 (rebranded Nexcom devices)
- Barracuda F12 / F18 / F80 (older revisions were made by Nexcom, newer ones, by Aewin)
- AppNeta m50 and m70 (rebranded Aaeon devices)
- If you get lucky, you could stumble into an affordably priced Lanner NCA-1513 or even NCA-1515 (this post was written about the 1515, but it applies to the 1513 as well)
Please note that secondary market prices tend to fluctuate. Often (though not always), there’s this one seller who just wants the device gone (usually, a user of stock firmware who upgraded to a newer device and doesn’t know what to do with the old one). So some eBay trawling may be needed to find that seller and their wares.
Non-x64 ideas:
- Luxul ABR-4500 and XBR-4500 (specifically the 4500 models; there are 4400 and 5000 models that look very similar, but OpenWrt is not available for them, so read the sticker on the bottom of the device carefully). These are interesting for some use cases because they have integrated power supply (no power brick; the device plugs directly into the wall) and occasionally come with rack mounts, even though they are very much desktop-size.
- Ubiquiti ER-Lite / ER-4 / USG. Compact, passively cooled. ER-4 has an integrated power supply. Out of the box, perform poorly, but once you enable offloading and packet steering, things improve drastically.