AN MD80 IN TKOF AND CLB INDICATED OVERWT CONDITION. PERFORMANCE CALCULATIONS REVEALED MAX WT OF ACFT WAS EXCEEDED.

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MY FIRST INDICATION OF A HVY WT CONDITION WAS THE LENGTH OF RWY NEEDED FOR OUR TKOF ROLL IN ZZZ; FOLLOWED BY 'SPD LOW' FLASHING ON INITIAL CLBOUT. AT 7000 FT WE LEVELED AND AT 250 KTS THE ALPHA SPD WARNING WAS ON. I RAN THE SPD BUG UP A KNOT AT A TIME UNTIL IT WENT OUT AT 255 KTS. 'MIN MAN' FOR OUR CLOSEOUT WT SHOULD HAVE BEEN 249 KTS. 255 KTS CORRESPONDS TO 154000 LBS ACCORDING TO THE REF SPD CARDS. THIS FAR EXCEEDS THE MAX WT OF THE ACFT. CLB PERFORMANCE WAS MEDIOCRE. AT FL290 WE NEEDED 1.78 EPR TO HOLD .76 MACH (SURFACE AIR TEMP -45 DEGS; RAM AIR TEMP -18 DEGS; TRUE AIR SPD 447 KTS). FUEL IN THE TANKS 28200 LBS FF 3700 LBS/HR. WE HAD CORRESPONDINGLY HIGH ALPHA SPD INDICATIONS ON APCH AND LNDG. I PADDED OUR SPDS TO EQUAL 134000 LBS. I CALLED FOR AN OFF LOAD AUDIT AND AN OVERWT LNDG INSPECTION AS WELL. ALTHOUGH THE MAIL WT VERSUS THE BAG COUNT DISCREPANCY WAS NEGLIGIBLE I HAVE THESE OBSERVATIONS. IT WAS 'CRUISE' DAY WITH MANY OVERSIZED BAGS THAT WERE NOT ANYWHERE NEAR 30 LBS A PIECE. CARRY ON LUGGAGE WAS AS LARGE AS THE PEOPLE THAT BROUGHT IT. PEOPLE CONTINUING ON TO THE ISLANDS OR S AMERICA ARE KNOWN TO BRING LARGE AMOUNTS OF AMERICAN GOODS THAT ARE HARD TO COME BY IN THEIR OWN COUNTRIES. DIVERS TO CARIBBEAN WATERS CARRY HVY EQUIP. SOLUTIONS MAY INCLUDE DOING A MULTI-DAY AUDIT WHERE EVERY BAG IS WEIGHED AND COUNTED INCLUDING CARRY-ON ITEMS FOR FLTS TO AND OUT OF ZZZ1 AND YES HAVING PEOPLE STEP ON THE SCALE AS WELL. MY FEELING THAT IN CERTAIN MARKETS 170 LBS MAY NOT BE A REALISTIC FIGURE.