The line speed on an Iris graph is taken from the configured interface speed on the router.
Should the line speed on the router change, the graphs will display the line speed change. You might, however, have to zoom to the time that the line speed changed.
For example, if you have recently updated the line speed, you will only get an accurate line speed reflecting on the graph if you zoom into the time period from when the line speed was updated.
The bandwidth statement and the graph might not always match up. This could be because of the way you are viewing the graph. If you zoom into the most recent time period on the graph, the line speed on the graph will now be correct.