OpenVPN: Windows 7-10 client vs Linux Mint 20.01 client

Are this setting for win client and IPfire server still valid?

sndbuf 393216
rcvbuf 393216
push “sndbuf 393216”
push “rcvbuf 393216”

How to add this setting permanently to ovpn.conf, every time i save openvpn with gui button, setting are deleted?

Linux Mint client is flaying with 6 MB/s or more on both directions.

Win7-10 are struggling with 2.5 M MB/s or less. Tested on the same laptop and openvpn for Win are different releases from last year.
Same settings:

Actually Win 10 and release OpenVPN 2.5.1. is in the middle with 4 MB/s. It uses much more cpu than Win 7.