To tag on to Ulf's message. As long as you are in path with the AMD, you could use the auto-discovery in DC RUM (12.3+) to identify who is talking to it and get your RTT and volume based metrics when going to Microsoft's cloud.
If I remember from talking to a Microsoft performance consultant, a lot of their expectations are determined by distance from their public POP (point of presence). In other words, if you can prove the RTT to their POP is within a certain value, you could identify whether it was an issue of the path to O365 or O365 itself. As Ulf said though, synthetic would give you that constant measure, but if you already have an AMD in path it never hurts to have the real-user data as well.