CTLED FLT TOWARD TERRAIN IN A A-320. ALTDEV ALT OVERSHOT IN DSCNT. GPWS WARNING IGNORED. FO; PF; ATTEMPTED TO DSND LOWER THAN CLRED BECAUSE OF 'CLEAN PERFORMANCE' OF ACFT.

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DSNDING INTO LOW SUN SETTING DIRECTLY IN OUR FACE. COULD SEE PDX ALONG SIDE COLUMBIA RIVER ABOUT 30 MI OUT AT 8000 FT. STARTED DSCNT SOON AFTER VISUAL APCH CLRNC ISSUED. APCH CTL STATED; 'CLRED FOR VISUAL APCH TO RWY 28L; MAINTAIN 2000 FT UNTIL 7 NM FROM PDX' WITH THE SUN MAKING IT HARD TO SEE THE RWY AND DISTORTING DISTANCES; I WAS VFR BUT USING MOVING MAP DISPLAY (ND) FOR RWY REF. THE AIRBUS 320; BEING A VERY CLEAN ACFT; IS HARD TO SLOW AND DSND AT THE SAME TIME. ABOUT 22 MI OUT I DECIDED TO 'SCOOT' ON DOWN TO 2000 FT AND 'MOTOR' INTO THE RWY FROM THERE. I WAS DSNDING AT ABOUT 2800 FPM. AT AROUND 4000 FT WE START GETTING 'TOO LOW TERRAIN' GPWS AND 'SINK RATE.' I SLOWED THE DSCNT SLIGHTLY; BUT SINCE THE RWY WAS IN SIGHT AND NO OBVIOUS REAL ESTATE OBSTRUCTION BTWN US AND THE ARPT; WE CONTINUED ON DOWN...THINKING THE WARNING WAS SPURIOUS. THE GPWS STAYED ACTIVE. AT ABOUT 3500 FT; I LOOKED AT THE RADAR ALTIMETER AND IT SHOWED 1800 FT AGL. I DISCONNECTED THE AUTOPLT AND RETURNED TO 4000 FT WHILE THE APCH CTL INQUIRED ABOUT OUR ALT. HE ASSUMED SINCE WE SAW THE RWY THAT WE WOULD CLR ALL TERRAIN; BUT WITH THE SUN REDUCING VISUAL ACUITY; AND NOT LOOKING AT MINIMUM SAFE ALT CHART; WE COULD HAVE DSNDED VERY VERY CLOSE BEFORE WE BECAME AWARE OF THE TERRAIN.