OpenVPN Performance weirdness

Hi All,

I've got OpenVPN up and running on my Centos 6 Linode in Newark which is working fine for what I need, however, I've noticed some weird performance issues when I try to stress test it (speedtest.net through VPN with various geographically local to Linode servers). I'm getting much higher upload than download speeds from my client in the UK, and it seems that download over the VPN is being limited to about 5Mbps for some reason.

I tried installing the OpenVPN client on a Centos Box locally and tested from there, but no difference at all (also tried routing other LAN devices through it as a gateway). The normal Client I use is Windows 7 on a reasonably meaty i52500K@4.6GHz, 16GB RAM. CPU usage seems to be around 5% on the server when maxed out, and negligible on any client be it Windows or Centos. I've also tried using a different DSL router in case there was anything weird going on there.

Has anyone else come across this at all? it can't be an outbound cap on the Linode because I can download files from the webserver on the same box at over 200Mbit/sec when not on the VPN.

I'm running UDP, dh 2048 bit key (shouldn't affect performance once the tunnel is up?), default cipher, lzo compression is on both sides.

The only things I can think of that are left to try are disabling compression/cipher or to change the port and/or protocol the server is listening on in case my ISP connection (BT Infinity) is throttling for some reason. I can't try those until I get home so I was just wondering if anyone else has any ideas?

Thanks in advance for any advice!