They will be very erratic - power will change constantly depending on terrain, wind, your pedal action etc etc.
I use a 705 and typically have it show the 3 sec av and 30 sec av display when riding intervals etc with it. If you go into the Settings menu you will see the Data Fields and from the lists there you have a variety of power related options. Av lap power might also be useful for intervals as well, but its worth experimenting a little and seeing what works for you.