AN FO RPT ON A SPD DEV DURING AN ENCOUNTER WITH MODERATE CHOP OVER THE ROCKIES 100 MI NW OF DEN; CO.

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WE ENCOUNTERED LIGHT TO MODERATE CHOP OVER THE ROCKIES ENRTE TO ORD FROM LAX. THE CAPT ASKED ME TO ASK ZAB FOR HIGHER (FL370). ZAB ASKED US IF WE COULD ACCELERATE TO .81 MACH (WE WERE AT .80 MACH). CAPT INSTRUCTED ME TO REPLY IN THE AFFIRMATIVE. WE ACCELERATED TO .81 MACH. SHORTLY AFTER; THE ACFT HIT A POCKET OF MODERATE CHOP; SENDING OUR AIRSPD INTO THE OVERSPD WARNING MOMENTARILY. CAPT BEGAN DIALING BACK THE AIRSPD. I ASKED IF HE WANTED ME TO SAY ANYTHING. HE ANSWERED THAT WE WOULD ACCELERATE BACK TO .81 MACH IN A FEW SECONDS. ABOUT 5 MINS LATER; WHILE THE CAPT WAS ADJUSTING OUR AIRSPD; ATC INQUIRED AS TO OUR AIRSPD. THE CAPT RESPONDED; 'TELL THEM WE'RE DOING .80 MACH.' (WE WERE FLYING AT .78 MACH.) NEXT; ZAB GAVE US A CLB TO FL370. WE BEGAN OUR CLB. WHILE IN THE CLB; WE WERE AT .74 MACH. ZAB INSTRUCTED US TO DSND BACK TO FL330 AND LECTURED US ON THE IMPORTANCE OF MAINTAINING ASSIGNED AIRSPD. PRIOR TO INITIATING THE CLB; THE CAPT ATTEMPTED TO ACCELERATE TO .81 MACH AFTER ATC INQUIRED ABOUT OUR AIRSPD; AND ONCE AGAIN WE GOT A MOMENTARY OVERSPD WARNING DUE TO MODERATE CHOP. I FELT; IN THIS CASE; WE SHOULD HAVE INFORMED ATC THAT WE COULD NOT MAINTAIN .81 MACH DUE TO EXISTING CONDITIONS. THE CAPT WAS CONTINUALLY ADJUSTING THE AIRSPD WITH THE INTENTION FO ACCELERATING BACK TO .81 MACH BUT CONDITIONS PREVENTED THIS FROM BEING POSSIBLE. OTHER FACTOR: HIGH TIME CAPT AND LOW TIME PROBATIONARY FO.