There have been several cases where I have seen over 100% utilization on a loopback interface. I have also noticed that Orion has detected the loopback interfaces as being 10Mbps. If it's capable of going above 100% utilization it seems that it's more likely a 100Mbps interface.
I realize that the loopback interface exists purely in software so is this a case where it (Microsoft) just throws out a value for it's speed to give you something but in reality it's capable of running at any speed necessary?