I have a VPN setup between a remote office with 2 ADSL connections (8Mb downstream, 512Kb upstream) and a main office with a 10Mb EFM connection (10Mb both up and down).

The VPN is an IPSec connection using a DrayTek 2930 router for the ADSL and a DrayTek 3200 router at the EFM end. However, I'm unable to get speeds over this connection (tested with iperf) of anything over 600Kb or so down from the main office (traffic will pretty much always be from the main office to the remote office)

Whilst I realise that there is an overhead and I'm never going to get the "full" bandwidth available over this VPN, I'd like to think that there's something I should be looking at that may help improve it.

I've tried using the DrayTek's built-in "VPN Trunking" features which are supposed to load-balance connections, but this doesn't seem to improve matters much.

I guess my question is - is this the kind of performance I should expect from this kind of setup and I'll just have to live with it, or should I be able to squeeze something more out of it through some VPN magic?