ALT DEV ALT EXCURSION.

Narrative

WHILE BEING RADAR VECTORED FOR AN APCH TO OAK THE PF (CAPT) WAS HANDLING ATC; WHILE PNF (FO) WAS DOING A PA TO THE PAX. SOME COM WAS CONFUSED OR MISUNDERSTOOD AND THE ASSIGNED ALT WAS UNCERTAIN. 9000 FT WAS SET ON THE ALT ALERTER; BUT THE PF UNDERSTOOD THAT 7000 FT WAS THE LAST ASSIGNED ALT. WE HAD DSNDED TO 8500 FT BEFORE A DISCUSSION BTWN THE PF AND PNF REGARDING THE LAST ASSIGNED ALT WAS. IT WAS DETERMINED TO REQUEST CONFIRMATION. NO IMMEDIATE RESPONSE WAS RECEIVED FROM ATC. WE WERE FINALLY GIVEN 8000 FT WITH NO COMMENTS MADE. AS A RESULT; WE DO NOT KNOW IF ANY EXCURSION OR DEV WAS MADE. ATC WAS VERY BUSY AND WAS GIVING SPD; ALTS; HDG; TFC AND CLRNCS QUITE RAPIDLY. I CAN UNDERSTAND AND APPRECIATE THEIR WORKLOAD; HOWEVER TOO MUCH INFO; TOO FAST; IS NOT A GOOD COMBINATION AS CONFUSION AND MISINTERPRETATION CAN BE INTRODUCED. OVERALL; I FEEL THAT ATC DOES A COMMENDABLE JOB UNDER THEIR CIRCUMSTANCES. SUPPLEMENTAL INFO FROM ACN 314691: I THOUGHT WE WERE CLRED TO 7000 FT; SLOW TO 180 KTS. I SLOWED THE AIRPLANE; WHILE LEVELING OFF AT APPROX 9000 FT. THE FO DID NOT HEAR DSND TO 7000 FT; SO THE ALT ALERTER WAS SET AT 9000 FT. I THEN STARTED TO DSND TO 7000 FT AND THE ALERTER WENT OFF. I LEVELED OFF AT 8500 FT AND CLBED BACK UP TO 9000 FT. I ASKED THE FO TO VERIFY WE WERE CLRED TO 7000 FT. HE ASKED APCH WHAT OUR CLRNC ALT WAS (TWICE). ATC THEN RESPONDED; 'ACR X DSND TO 8000 FT; WE HAVE TFC BEHIND YOU AT 7000 FT.'