AN A320 HAS A TCASII RA TO AVOID AN NMAC WITH A KING AIR IN SJU CLASS E AIRSPACE.

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ON RADAR VECTORS FOR ARR INTO SJU; HDG 190 DEGS; LEVEL AT 3000 FT; VMC CONDITIONS. ALL OF A SUDDEN; NAV DISPLAY SHOWED A RED DIAMOND AT OUR 10 O'CLOCK POS; FOLLOWED BY ATC ADVISING TFC AT OUR 10 O'CLOCK POS; FOLLOWED BY AN RA 'TFC DSND;' FOLLOWED BY ATC ADVISING US TO CLB. BY THE TIME ATC ADVISED US TO CLB; WE HAD JUST STARTED OUR DSCNT; AUTOPLT DISCONNECT; FLT DIRECTORS OFF; JUST AS PER THE 'BOOK.' LOOKING UP; I COULD SEE THE PLTS IN THE KING AIR LOOKING DOWN AT US; MISSING US BY A COUPLE OF HUNDRED FT. I AM INCLUDING A TYPED NOTE I FEEL COULD HELP IN FUTURE RA'S LIKE THIS ONE. I HOPE YOU'LL CONSIDER MY SUGGESTIONS. AFTER HAVING EXPERIENCED A REAL LIFE RA; I WANTED TO RELAY SOME SUGGESTIONS. IN OUR PARTICULAR SIT; THE RA JUST 'POPPED-UP' AND WE DIDN'T HAVE MUCH TIME TO REACT. IT WAS A BRIGHT SUNNY DAY WITH CLOUDS AROUND; A DAY WHERE ONE HAD TO WEAR SUNGLASSES. THE AVOID MANEUVER IS BOTH A TRY TO VISUALLY ACQUIRE AND SEE ONE'S INSTS AND FLY AWAY BASED ON THE TCASII ADVISORY. I FELT THERE WAS TOO MUCH LAG TIME TO HAVE THE EYES ADJUST FOR THE CHANGING CONDITION OF A BRIGHTLY LIT BACKGROUND WITH SUNGLASSES ON AND A DARKENED INST PANEL. IN OUR SIT; WE LITERALLY HAD 1 TO MAX OF 2 SECONDS OF TIME TO REACT. FROM THIS EXPERIENCE; I WOULD LIKE TO SEE THE TCASII ADVISORY BE EXPANDED TO HAVE THE AURAL WARNING COMMAND A DSCNT/CLB RATE APPROPRIATE TO THE SIT. I FEEL THIS WOULD HAVE BEEN VERY HELPFUL IN BOTH AURALLY DETERMINING JUST HOW FAR THE TFC IS WHILE VISUALLY TRYING TO ACQUIRE; PLUS EMPHASIZING THE SEVERITY OF THE SIT AT THAT MOMENT. SUPPLEMENTAL INFO FROM ACN 620443: ALMOST SIMULTANEOUSLY; ATC ISSUED A CLB CLRNC WHICH I IGNORED. OUR FLT OPS MANUAL (FOM) CONFIRMED THAT TCASII COMMANDS TAKE PRECEDENCE OVER ATC INSTRUCTIONS. I BELIEVE THAT A CLB WOULD HAVE RESULTED IN A COLLISION.