Router / BGP performance Hardware?

how compares performance on eg a CCR2004-1G-12S+2XS vs openwrt on a intel J5005 i386 cpu ?
use case is BGP over GRE tunnel ( to route a PI class-c network over different internet links )

Highly depends on software and you probably might want to look for a distro not targeting embedded devices.

by now , my plan (for different other reasons) is to use routerOS ( with mikrotik CCR2004-1G-12S+2XS or 2116-12G-4S+ )
or OpenWRT ( with intel J5005 or GX-222gc )
so i am looking for some hint how those two solutions might compare in performance
i want to stick with openwrt or routerOS

to route a PI class-c network over different internet links

Not enough data, need more details.

If you only import single default route from each transit, you can run BGP on ancient 32MB RAM OpenWRT router.

Working with full tables and multiple peers will require completely different hardware with quite a lot of RAM.

first step indeed is over a tunnel broker anouncing 1 network and not downloading all routes , but having a default route.
but next step is to change to a 1gbit line with bgp support and holding all tables in RAM

CCR2004-1G-12S+2XS = 4GB RAM
2116-12G-4S+ = 16GB RAM
on i386 RAM is no problem ether