Hi,
you can do this very simply with existing actions, get the speed, and the next action is a compare float, that fires an event if above a certain threshold.
Have you tried this already? I do that many times, and never felt the need to create a custom action for this actually, because it's so specific to a property that it's "better" to simply work on a generic float, so one action to get the float from the property, and then use some comparision tools on that float.
Bye,
Jean