I've tried a few things including tweaks to overcome the very limited performance of any PPP feature on the CCR but i wouldnt call it practical. It seems that any kind of VPN or PPP server has severly limited performance not only by being single threaded but in general.

The connections are also very unstable. After a minute of using the mikrotik bandwidth tester i had to reconnect the VPN just to be able to use it since everything timed out.

The mikrotik bandwidth tester topped out at around 150Mb/s (TCP) while using larger packets topped out at 300Mb/s (UDP) both ways. I have used ways around the performance problems but they arent practical and not something you would ask your clients to do (thankfully i dont have any) so i am able to get multi gigabt PPP/VPN performance off the CCR but with a lot of config.

There was no NAT or any firewall rules for VPN/PPP during testing and multiple instances of the bandwidth tester was used. I think this same problem effects other similar areas in routing and probably other routerboards too. I wouldnt mind working for mikrotik in the coding department to speed things up but my time is very limited.

The CCR is also more stable than windows under huge network stress but is just a side observation i noticed during testing.

What packet size did you use for UDP?
Did you have change-mss for TCP traffic?
What RouterOS version do you use? latest?

Also i do not think it is best idea to test CCR performance with just one connection, it is kinda breaking the point of multi-cpu systems
run many conenctions - download some popular torrent through the tunnel.

I used multiple connections to achieve higher throughput. Im talking about PPP performance in general on mikrotik which seems more like a coding problem rather than the device. I say this because when stress testing PPP performances PPP/VPN disconnects. Using larger packet sizes does increase bandwidth throughput but not linearly.

Using a torrent wont increase the throughput. It only will increase the throughput on standard NAT.

i did change TCP-mss

i used routerOS 6.21

As i said i did overcome the throughput problem using multiple connections but it requires the client to configure for multiple links.