AN ACR LANDED BELOW MINIMUMS IN RAPIDLY DETERIORATING WX CONDITIONS.

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WX AT SEA HAD BEEN VARIABLE FOR SOME TIME - FROM RVR 1000 VARIABLE 1400 TO NEAR VFR. IT WAS FO'S LEG AND SEA ATIS RPTED 1 1/2 MI VISIBILITY. APCH REQUESTED OUR RVR REQUIREMENTS; AND WE RESPONDED 700 FT (CAT IIIA). NO MENTION WAS MADE AT THAT TIME OF ACTUAL RWY 16R RVR. ATIS STILL RPTED 1 1/2 MI. ON DOWNWIND APCH RPTED RWY 16R RVR AS 700-800-1100 FOR TKOF; MID; AND ROLLOUT. SHORTLY THEREAFTER WE WERE TURNED ON BASE. THE WORKLOAD INCREASED SIGNIFICANTLY AT THAT POINT AS WE SHIFTED PF AND PNF RESPONSIBILITIES. THE BASE LEG WAS RELATIVELY SHORT. WE SHOULD HAVE REQUESTED VECTORS TO GIVE US MORE TIME TO SET UP. WE WERE SHIFTED TO TWR FREQ; AND WE BELIEVE THE TRANSFER SWITCH WAS MOVED. EITHER IT WAS MOVED OR IT WAS INADVERTENTLY SWITCHED BACK TO APCH. ON SHORT FINAL; I COULD NOT REMEMBER RECEIVING LNDG CLRNC; AND AT THE SAME TIME THE FO CALLED APCHING MINIMUMS' AND 'I HAVE THE STOBES'. I REQUESTED LNDG INFO. AT THAT POINT I HAD GOOD VISUAL ON THE RWY. TWR RESPONDED WITH LNDG CLRNC. IT SIMPLY DID NOT REGISTER AT THE TIME; BUT IN RETROSPECT; THE FO AND I BELIEVE THE TWR HAD SAID '...RVR 600....' WE ARE SIMPLY NOT SURE IF THE 600 READING REFERRED TO TKOF; MID; OR ROLLOUT. I MIGHT HAVE ANTICIPATED THE SIT BETTER AND BEEN BETTER PREPARED FOR THE VARYING CONDITIONS. WHILE I REALIZE THE ATC SYS IS OFTEN OVERLOADED; THE COCKPIT OF A 2 PLT AIRPLANE CAN QUICKLY BECOME OVERLOADED AS WELL. IT IS IMPERATIVE THAT ATC PROVIDE ACCURATE AND TIMELY INFO.