Possible Fuel Pressure Problem?

I have recently noticed that my fuel pressure gauge will spike up to 65-70 psi while idling and then fall back down to around 38-40 psi. It seems to happen after driving for atleast 30-45 minutes. I haven't noticed any difference in performance though; idle, acceleration, etc are all normal. Is this a normal deal or is something possibly wrong?

This leads me into my next question, what should the fuel pressure be at for a 2.1 Intercooled GT @ idle, with boost, etc? What are the danger zones (too low and too high pressure)?

Thanks