C90 APCH CTLR MISJUDGED SPACING BTWN A B757 AND A REGIONAL JET RESULTING IN A GAR.

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ARRIVING INTO CHICAGO AIRSPACE; WE WERE LEADING THE PACK AND GIVEN 310 KTS OR BETTER. WITH APCH CTL; WE WERE GIVEN CROSS BIFLE AT 7000 FT; CLRED THE APCH ILS RWY 14R; 250 KTS FOR NOW. PRIOR TO SEXXY; WE WERE TOLD TO STAY ON THE LOC BUT MAINTAIN 6000 FT. THEN WE WERE TOLD TO REDUCE TO 170 KTS. AT THAT POINT; I SAW THE REASON. WE HAD AN RJ TURNING IN 1 MI AHEAD OF US. I RPTED TFC TO APCH AND QUERIED IF THAT WAS OUR SEQUENCE NOW. HE REPLIED YES; AND GAVE US A FURTHER AIRSPD REDUCTION TO OUR FINAL APCH SPD. HE THEN TOLD THE OTHER GUY TO MAINTAIN 210 TO THE MARKER. WE WERE THEN CLRED TO DSND ON THE ILS AGAIN. AT 3500 FT; WITH ONLY 1.5 MI IN TRAIL OF THIS GUY; AND 500 FT ABOVE THE CLOUDS; IT WAS APPARENT TO US THIS WAS NOT GOING TO WORK OUT AND WE BROKE OFF THE APCH. REMARKS FROM APCH INDICATED OUR CTLR PLANNED ON THE SEQUENCE; BUT THE SHIP BEING PLACED AHEAD OF US WAS SLOW IN THEIR TURN OR DID NOT REACT AT THE PACE THE CTLR EXPECTED. I BELIEVE IT SHOULD HAVE BEEN APPARENT THAT THIS WAS NOT GOING TO WORK OUT; AND WONDER IF THE AIRPLANE BEING VECTORED INTO THE SEQUENCE SHOULD HAVE BEEN GIVEN THE GAR. FORTUNATELY; WE WERE STILL WELL AHEAD OF SCHEDULE. I DON'T NEED TO MENTION FUEL WASTE WITH THIS EVENT.