B733 VECTORED TO ATL RWY 26R FINAL 3 POINT 5 MI BEHIND A SLOWING B757. B733 REDUCES ASSIGNED SPD; IS UNABLE TO ADVISE ATC. B733 PULLED OFF FINAL BY A80; AND ADVISED TO CALL FACILITY.

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WE ARRIVED VIA THE MACEY ARR; AND WERE BEING VECTORED FOR AN ILS LNDG ON RWY 26R. WE WERE ASSIGNED A SOUTHERLY HDG FOR THE INITIAL VECTORS AND THEN TURNED SW FOR THE INTERCEPT. VISIBILITY INTO THE SUN WAS DIFFICULT TOWARD THE ARPT. THE FINAL APCH CTLR POINTED OUT TFC ON THE FINAL APCH COURSE (A B757); WHICH WE ACKNOWLEDGED. WE IDENTED THE B757 ON THE TCASII; AND CONFIRMED THAT INFO VISUALLY. THE CTLR THEN CLRED US A VISUAL APCH TO RWY 26R TO FOLLOW THE B757. AT THIS POINT; WE INTERCEPTED THE RWY 26R ILS COURSE AND PROCEEDED INBOUND. THE CTLR TOLD US TO MAINTAIN 170 KTS UNTIL AJAAY (THE FAF). THE TCASII AT THIS POINT SHOWED THE B757 ABOUT 3-3.5 MI AHEAD OF US; AND WE WERE ABOUT 10 MI FROM THE ARPT. SOME TURB WAS ENCOUNTERED INTERCEPTING THE FINAL APCH COURSE BEHIND THE B757; AND WE DECIDED TO INCREASE THE SPACING SLIGHTLY SINCE WE THOUGHT THE SAFE SPACING INTERVAL WAS 5 MI BEHIND A 'HVY.' WE OFFSET SLIGHTLY FROM THE FINAL APCH COURSE AND SLOWED TO 140 KTS TEMPORARILY; AND THE SPACING ON THE TCASII INCREASED TO 4-4.5 MI. BEFORE WE COULD CONTACT THE CTLR TO ADVISE OF THE TEMPORARY SPD CHANGE (DUE TO FREQ CONGESTION); THE CTLR ASKED US WHAT OUR SPD WAS. I REPLIED 140 KTS; AND THAT WE WERE TRYING TO GET SOME SPACING ON THE 'HEAVY' AHEAD OF US. HE REPLIED THAT IT WASN'T A 'HVY;' AND TOLD US TO BREAK OFF THE APCH AND TURN TO A 360 DEG HDG. HE NEVER GAVE US THE OPPORTUNITY TO INCREASE OUR SPD AGAIN. AT THIS POINT; THE B757 WAS STILL SHOWING ABOUT 4-4.5 MI AHEAD OF US ON THE TCASII. WE LEVELED AT ABOUT 4500 FT MSL AND CLEANED UP THE ACFT. THE CTLR VECTORED US IN A R-HAND BOX PATTERN; AND WE WERE CLRED FOR ANOTHER VISUAL APCH TO RWY 26R. UPON LNDG; THE GND CTLR ASKED US TO CALL THE APCH CTL FACILITY.