Any chance you don't have stock wheels on mate? If your profile is not correct, this would throw out the speedo and the speed you think you are doing is not actually correct. Not much difference between 110-122 if this is the case.
Not saying the cop was correct, but have you thought about this scenario? That you were in fact doing that speed and just didn't know it? I know we always firstly jump to the conclusion that cops suck, but just have a think about it for a sec and rule that out.
Speed matching at 60 is not going to be the same at highway speeds, get it checked, or post up your wheel/tyre sizes and someone smarter than me will be able to tell you if this is the case.