Ladies and gentlement:
Thanks to @Flx i was able to up the speeds a bit more:
Using the new wintun beta of openVPN 2.5 I'm now at slightly above 500mbps.
-Link to openVPN 2.5: http://staging.openvpn.net/openvpn2/
See here:
Basically you just need to install the new 2.5 openvpn version, start openVPN as administrator (!) and add the following line to the conf file:
windows-driver wintun
- i some how had to put it as one of the last point or it would give me some cryptic errormessage, also it didn't work in combination with "auth sha512" as suggested in the forementioned post.
So thank you again @Flx!
EDIT: Completely Idle Frankfurt Mirfak delivered >570mbps: https://deutsche-glasfaser.speedtestcustom.com/result/7cea7f20-5c60-11ea-8fed-e3d7efa295ff
Neat 😎