B737-700 FLT CREW DECLARES MIN FUEL UPON ARR AT DEST.

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FLT TO LAS. INITIAL DISPATCH RELEASE SHOWED A NON-STANDARD ROUTING DUE TO UPPER LEVEL HEADWIND CONCERNS. ATC CLRNC DELIVERY; HOWEVER; ISSUED ROUTING COMPLETELY DIFFERENT THAN WHAT WAS FILED SO CAPT DECIDED WISELY TO CONTACT DISPATCH AND HAVE THEM RE-COMPUTE THE FUEL BURN. DISPATCH THEN TOLD CAPT TO DISREGARD INITIAL ROUTING AND THAT THEY WERE GOING TO RE-FILE THE STANDARD COMPANY RTE INSTEAD. BASED ON MY DISCUSSION WITH CAPT; DISPATCH INFORMED HIM THE NEWLY COMPUTED ARR FUEL FOR THE STANDARD RTE WOULD NOW BE 5.6K LBS. NO NEW RELEASE FORM WAS GENERATED. ONCE AIRBORNE THE CAPT AND I REALIZED THE REAL TIME FUEL BURN WAS STARTING TO EXCEED WHAT WAS PREDICTED. THE OPC MAX RANGE ECON PROFILE WAS FLOWN. AROUND THE LNK VOR; CAPT ACARS'D DISPATCH ASKING THEM TO RE-COMPUTE ARR FUEL. DISPATCH RESPONDED AND ENSURED US WE WOULD LAND WITH 5.0 SO WE CONTINUED TO PRESS ON TO LAS. FUEL BURN WAS STILL HIGHER THAN PLANNED DUE TO WINDS. THERE WAS NO UNNECESSARY VECTORING BY ATC. REALIZING WE WERE GOING TO LAND BELOW 5.0; CAPT DECLARED MIN FUEL WITH APCH. WE LANDED WITH APPROXIMATELY 4.3K LBS AND SHUT DOWN WITH 4.1K LBS. AS FOR PRIORITY HANDLING; I DO NOT BELIEVE WE RECEIVED ANY BASED ON JUST THE MIN FUEL DECLARATION VS EMER. ALSO; APCH TOLD US WE WERE NUMBER 6 IN LINE TO LAND ON RWY 25. SO TO SUMMARIZE: 1) WHY THE LAST MINUTE RE-ROUTE FROM DISPATCH? FROM THE INITIAL RELEASE FORM; WE ACTUALLY HAD A 6.7 PLANNED ARR FUEL. 2) WHY WAS DISPATCH'S FUEL BURN RE-COMPUTATION RECEIVED AIRBORNE OVER LNK SO OPTIMISTIC? WE LANDED 700 LBS BELOW WHAT WAS PREDICTED AND HAD TO DECLARE MIN FUEL. 1) WHEN THERE'S A MAJOR RE-RTE FROM WHAT WAS ON THE DISPATCH RELEASE; GET DISPATCH TO GENERATE A NEW RELEASE FORM. 2) DISPATCH'S FLT PLANNING SYSTEM (ESPECIALLY WINDS ALOFT) NEEDS TO BE LOOKED AT. WHY WERE THEIR COMPUTATIONS SO OPTIMISTIC.