MD80 FLT CREW DIVERTS FOR FUEL CONSIDERATION.

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BEFORE DEP I NOTICED WE WERE FLT PLANNED AT APPROX 25000 LBS OF FUEL FOR OUR ALL-NIGHTER TO ORD. THIS SEEMED LIKE A VERY LOW FUEL LOAD AND I EXPRESSED MY CONCERN TO THE CAPT. HE SAID HE THOUGHT THIS WAS A REASONABLE LOAD; ALTHOUGH I DISAGREED. FOR THIS FUEL LOAD TO WORK WE WOULD HAVE NEEDED OPTIMUM CONDITIONS; IE BEING ABLE TO CLB TO FL370 IMMEDIATELY AFTER DEP; HAVING THE FORECASTED WINDS; AND BEING ABLE TO STAY AT FL370 FOR THE ENTIRE FLT. ON TAXI-OUT OUR CLOSEOUT INDICATED WE HAD PICKED UP AN ADDITIONAL 10 TO 15 PAX; AND OUR GROSS WT INCREASED APPROX 3000 LBS. AFTER DEP WE WERE NOT ABLE TO CLB TO FL370 BECAUSE OF OUR INCREASED GROSS WT. WE WERE NOT ABLE TO CLB TO FL370 FOR ABOUT 45 MINS TO 1 HOUR AFTER DEP. FOR SOME INEXPLICABLE REASON; THE CAPT CHOSE TO FLY AT .760 MACH INSTEAD OF THE FLT PLAN .740 MACH. I ASKED HIM WHY HE WAS CRUISING AT LESS THAN OPTIMUM SPD; AND HE BACKED IT OFF TO .75. I AGAIN EXPRESSED MY CONCERN THAT WE WOULD NOT HAVE ENOUGH FUEL TO MAKE IT TO ORD. HE SAID HE WOULD WATCH IT. THE FORECASTED WINDS NEVER MATERIALIZED; AND RATHER THAN HAVE 90 TO 100 KTS TAIL WINDS; OUR ACTUAL TAIL WINDS AVERAGED ABOUT 68 KTS. AS WE PASSED EACH FIX; WE WERE DOWN ABOUT 100 LBS; AND IT BECAME EVIDENT ABEAM ICT THAT AT THAT POINT WE WERE DOWN 1300 LBS AND AT THE CURRENT RATE; WOULD LAND ORD AROUND 4000 TO 4500 LBS. AT THIS POINT THE CAPT ELECTED TO DIVERT TO MCI TO GET MORE FUEL. ALL OF THIS COULD HAVE BEEN AVOIDED BY PUTTING ON AN ADDITIONAL 2000 LBS. THERE WEREN'T ANY WT RESTRS; SO ADDING FUEL WOULD NOT HAVE BEEN A PROB.