*This is only supposed to be temporary*
I set up a cron to download the 1G internode test file every 30 min.
This is monitoring the interface with snmp which is polled at 1min interval, so I offset the start time of the download by 30 seconds so there is always a full minute downloading. This then shows the monitored download speed at 1min resolution. I think this is better than timing it directly because it shouldn't be affected by "other things using the network".
Seems to show that ping is strongly related to the poor download speeds (I should probably turn off that cron job now)