B757 LNDG MDW SLOWS ON FINAL; FOLLOWING ACFT ISSUED ATC GAR.

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WIND AT MDW WAS 150 DEGS AT 10 KTS; MAGNETIC. WINDS FROM 1000 FT AGL UP TO ABOUT 4000 FT WERE FROM 160 DEGS TO 170 DEGS AND 40 KTS. MY ACFT WAS ASSIGNED A SPD OF 160 KTS AND A NE HDG FOR A BASE LEG TO THE ILS RWY 13C. NEARING THE ILS COURSE; OUR CTLR ISSUED AN EASTERLY HDG TO JOIN THE ILS RWY 13C. AN ACFT BEHIND US IN THE SEQUENCE WAS ASSIGNED A SIMILAR INDICATED AIRSPD; BUT I SUSPECT THEY WERE FAST BECAUSE ATC GROUSED TO THEM ABOUT BEING FASTER THAN SOMEONE ELSE RPTING THE SAME INDICATED AIRSPD A FEW MINS EARLIER. MY ACFT JOINED THE ILS AND; AT THE FACEL WAYPOINT; BEGAN TO SLOW TO 123 KIAS (VREF + 5 KTS). MDW TWR ASKED US TO INCREASE OUR SPD. I RESPONDED WITH 'UNABLE' SINCE WE WERE AT THE REQUIRED AIRSPD FOR OUR CONDITIONS. THE FASTER ACFT BEHIND US WAS TAKEN OUT OF THE APCH SEQUENCE AND RE-VECTORED TO THE ILS RWY 13C. NOTE THAT OUR ACFT WAS EXPERIENCING A STRONG QUARTERING TAILWIND ON THE BASE LEG (GND SPD ABOUT 180 KTS); THEN A STRONG QUARTERING HEADWIND ON FINAL APCH (100 KTS GND SPD BY THE TIME WE REACHED VREF + 5 KTS). THE TRACON CTLR SOUGHT A PHONE CONTACT AFTER LNDG; AND WE DISCUSSED THE CLRNC (160 KIAS TO FACEL) AND MY FLT'S ADHERENCE TO IT. SEPARATION COULD HAVE BEEN BETTER MAINTAINED IF THE GS CHANGE FROM BASE TO FINAL APCH WOULD HAVE BEEN ANTICIPATED. ADDING ANOTHER COUPLE OF MI BEHIND AN ACFT GOING FROM TAILWIND TO HEADWIND TO A SLOW FINAL SHOULD BE STANDARD PRACTICE. MDW HAS SHORT RWYS; WE CAN'T GO FASTER THAN VREF +5 KTS WITHOUT RISKING AN OVERRUN. DECELERATION MUST START AT THE FAF WAYPOINT; SINCE WE'RE DOING 160-170 KTS; AND THAT IS WELL ABOVE THE 120-130 KTS NEEDED FOR A LIGHTLY LOADED B757.