CESSNA 310 PLT DISAGREES WITH CTLR OVER ASSIGNED ALT.

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DULLES APCH CLRED ME AT APPROX 4000 FT MSL TO CLB TO 12000 FT 'WITH GOOD RATE THROUGH 8000 FT.' I READ THIS BACK AND CONTINUED MY CLB. '12000 FT' WAS WRITTEN ON MY FLT LOG WHICH I USE FOR ALL IFR FLTS. HANDED OFF TO ZDC WHEN I WAS APCHING 10000 FT. CALLED ZDC AND INCLUDED '10000 FT CLBING 12000 FT' USING PROPER NUMERAL PRONUNCIATION (EG; 1-0-THOUSAND CLBING 1-2-THOUSAND) WAS GIVEN ALTIMETER AND READ BACK ALTIMETER SETTING. AT 10500 FT ZDC CTLR ASKED MY ALT. TOLD HIM 10500 FT CLBING 12000 FT. HE ASKED ME IF DULLES APCH CLRED ME TO 12000 FT AND I RESPONDED AFFIRMATIVELY. SHORTLY THEREAFTER A FEMALE CTLR CAME BACK AND INFORMED ME THAT DULLES APCH ONLY CLRED ME TO 10000 FT. I DISAGREED AND REMINDED THEM THAT ON MY CALL-UP TO ZDC I ALSO INFORMED THEM THAT I WAS CLBING TO 12000 FT. IT SHOULD ALSO BE NOTED THAT MY INITIAL CLRNC (RECEIVED AT MANASSAS 'HEF WAS INITIAL 3000 FT EXPECT 12000 FT IN 10 MINS. THE ZDC CTLR STATED (LATER) THAT I SHOULD NORMALLY EXPECT ONLY 10000 FT BY DULLES APCH (FOR FUTURE REF). THIS BOTHERS ME; IF I HAD A RADIO FAILURE I WOULD BE EXPECTED TO CLB TO 12000 FT (IN DULLES AIRSPACE). SINCE I WAS TOLD TO EXPECT 12000 FT HAVING RECEIVED A 'CLB TO 12000 FT' DID NOT SEEM INAPPROPRIATE. WITH REGARD TO HUMAN PERFORMANCE FACTORS; I FIND THAT DULLES APCH IS ALWAYS BUSY AND THAT THEY SPEAK MUCH FASTER THAN MOST. I CAN KEEP UP AND FIND I; TOO; MUST SPEAK JUST AS QUICKLY IN ORDER TO NOT TIE-UP THE RADIO FREQ. WHEN SPEAKING THAT FAST; WE MAY TEND TO 'HEAR' WHAT WE WANT TO HEAR. I DON'T THINK MY UNDERSTANDING OF A CLB TO 12000 FT FROM THE DULLES CTLR WAS INCORRECT. I'M NOT PERFECT ALL THE TIME. BUT; WHEN I CHKED IN TO ZDC THE CTLR COULD HAVE CAUGHT THE DISCREPANCY IN TIME.