The CPU in my box is
CPU Type Intel(R) Celeron(R) CPU 3865U @ 1.80GHz
2 CPUs: 1 package(s) x 2 core(s)
AES-NI CPU Crypto: Yes (active)
QAT Crypto: No
It does ok, no issues. The netgate devices use ARM processors, so it doesn’t have to be very powerful for a home user with a moderate internet connection. Mine is a dual core, not so sure I would gain much benefit in a quad core.
If you end up using old kit, it’s likely you’ll spend more money on electricity.
The OpenVPN is rock solid on pfSense, you won’t have any issues.