Couldn't be bothered to wait till the w/e...
Have just tried removing OpenVPN from the equation, reverting to plain old vanilla webdav over port 80. The upload problem
disappears, with the speed being as good as I would expect from the decrepit ADSL line (40KB/s). More importantly, the uploads continue to completion, whereas over the VPN they would suddenly get extremely slow (<3KB/s) after approx 200K and would eventually crap out, rarely getting beyond 500KB. Small files were fine, and transfers in the other direction (server -> client) were great.
So I suppose I have to start troubleshooting OpenVPN. Any ideas, I've never used it before now... I have a faily basic setup - TAP-Win32, tun device, UDP. Could try disabling the VPN compression I suppose*.
Any VPN gurus out there?
Cheers
/s
*
ETA: Problem is not due to compression on VPN - just checked.