B767-300 FLT CREW REALIZED AFTER TKOF THAT THEY HAD DEPARTED WITH INCORRECT PERFORMANCE DATA.

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WHEN WE ARRIVED AT THE GATE FOR THE FLT; WE WERE TOLD THAT ALL FLTS WERE ON HOLD DUE TO A SUSPICIOUS BAG IN THE SCANNER IN THE BAG ROOM. NO BAGS WERE BEING MOVED NOR PAX LOADED UNTIL THEY COULD CLR THE BAG. THEN WE WERE TOLD TO WAIT FOR CONNECTING PAX. AFTER BOUT 1 HR 45 MINTS; WE WERE CLRED TO GO WITHOUT AN UNKNOWN NUMBER OF THE BAGS. IN THE MEANTIME; WE RECEIVED OUR WTS OVER THE ACARS PRINTER AND I NOTED THAT THE NEW WT WAS 25K LOWER THAN THE PLANNED WT (RED FLAG #1). I TOLD THE CAPT THIS AND WAS CONCERNED BECAUSE WE WERE GETTING CONFLICTING INFO ABOUT HOW MANY BAGS; CONNECTING PAX; AND CARGO WE WOULD LEAVE BEHIND. AS WE START TO PREPARE TO PUSH BACK; I SENT FOR NEW ATIS AND RWY DATA. THE RWY DATA STILL HAD THE 'P' FOR PLANNED BY THE WT (RED FLAG #2) AND I ANNOUNCED THIS BUT I DON'T THINK THE CAPT HEARD ME. RIGHT WHEN THIS WAS TRANSPIRING; THE PURSER CAME INTO THE COCKPIT TO TELL US THAT WE HAD 1 MORE PAX THAN SEATS. THE CAPT INSTRUCTED ME TO CALL OPS TO GET THE JETWAY BRIDGE BACK AND WENT BACK TO SEE WHAT THE PROB WAS. AFTER WE GOT THE EXTRA PAX OFF; WE PUSHED AND TAXIED QUICKLY BECAUSE WE WERE SO LATE. IT SHOULD BE NOTED THAT WE WERE ON DAY 4 OF A 4-DAY AND HAD GONE OVER 8 HRS OF FLYING DUE TO OPERATIONAL DELAYS ON DAY 1 AND DAY 3. I WAS; THEREFORE; TIRED AND SOMEWHAT FATIGUED (WOKE UP EARLY EVERY DAY) WHICH DULLED MY SENSES AND EYE FOR DETAIL. ON THE TAXI OUT DURING THE CHKLIST; I MUMBLED TO MYSELF THAT I SHOULD CONTACT LOAD PLANNING AS I DIDN'T GET THE 2 PREVIOUS RED FLAGS RESOLVED. HOWEVER; THE TAXI WAS SHORT AND TWR CLRED US TO TAKE OFF. SINCE IT WAS MY LEG; ON THE TKOF ROLL I ANNOUNCED THAT; 'I DON'T TRUST THE WTS; I'M GOING TO ADD SOME KTS AND ROTATE SLOWLY.' IN MY MIND I WAS GOING TO ROTATE AT THE ORIGINAL PLANNED VR OF ABOUT 140 KTS AND WATCH OUT FOR A MISTRIMMED ACFT. THE AIRPLANE FLEW FINE AND SOME NOSE-UP TRIM WAS NEEDED FOR BALANCED FLT AFTER LIFTOFF. A FEW MINS AFTER WE DID THE 'AFTER TKOF' CHKLIST THE CAPT NOTICED A PRINTOUT ON THE ACARS PRINTER WHICH WAS IN FACT OUR ACTUAL WTS. UPON FURTHER EXAMINATION; THE FIRST WTS WERE ACTUALLY FOR A DIFFERENT FLT. THE FLT WAS FOR ONE WE DID THE DAY PRIOR IN THE SAME TYPE OF ACFT. LESSON LEARNED: I ALWAYS ASSUMED THAT WHAT CAME OVER ACARS COULD ONLY BE FOR THE CORRECT FLT SO I DIDN'T HAVE THE HABIT OF CHKING THE FLT NUMBER AND CITY PAIR. I WILL NOW! I GOT TOO RUSHED AND NEVER STOPPED THE OP TO SATISFY MY CONCERN OVER THE RED FLAGS WHEN I COULD HAVE DONE SO. I ALSO DID NOT CLEARLY ARTICULATE MY CONCERNS TO THE CAPT. THIS WAS NOT DUE TO AN INABILITY TO SPEAK UP BECAUSE I AM USUALLY VERY VOCAL AND DO NOT HESITATE; BUT RATHER FROM BEING TIRED AND NOT UP TO MY USUAL PERFORMANCE. PROGRAMMING OF LOAD PLANNING ACARS MESSAGES SHOULD NEVER BE ALLOWED TO GO TO THE WRONG ACFT AND CERTAINLY NOT ON THE WRONG DATE AND CITY PAIR. IT ALSO SHOULD BREAK OUT CARGO AND BAGS LOADS FOR MORE CLARITY TO THE CREWS.