DEPARTING ACR-LGT CLIMBED TOWARD THE ALT OF ANOTHER ACR-LGT RESULTING IN LESS THAN STANDARD SEPARATION.

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WE WERE ON CLBOUT FROM RWY 27R IN ATL. CLRED TO 14000' AND IN A LEFT TURN TO 060 DEGS. PASSING ABOUT 9300' WE WERE CLRED TO 9000'. WE RPTED ABOVE 9000' AND STOPPED THE CLB AT ABOUT 9600'. AN ACFT FROM OUR RIGHT FRONT PASSED ABOVE AND IN FRONT OF US FROM RIGHT TO LEFT. SUPPLEMENTAL INFO FROM ACN 82772: WE BROKE OUT OF THE CLOUDS AND SAW WHAT WE BELIEVED TO BE AN LGT AT 10000' AND APPROX 200 YDS AHEAD OF US. NO EVASIVE ACTION TAKEN. AS TO WHY IT HAPPENED; I BELIEVE THERE WAS ONLY 1 CTLR WORKING DEP AND ARRS; AND HE HAD TOO MANY ACFT TO WORK SAFELY. THESE 2 ACFT WERE PLACED ABOUT 10 MI IN TRAIL WHEN THE FIRST ACFT ENCOUNTERED CHOP AND TURB. MLG X REDUCED HIS AIRSPD BY A FACTOR OF MACH 10. THIS SPD REDUCTION WAS UNANNOUNCED AND UNAUTH. LGT Y DID NOT REDUCE HIS SPD AT ALL WHEN FLYING THROUGH THE AIRSPACE WHICH MLG X HAD FLOWN THROUGH JUST 2 MINS BEFORE. THE PROB WAS DISCOVERED WHEN THE DIFFERENCE IN AIRSPDS WAS NOTICED. THIS SPD WAS AT TIMES IN EXCESS OF 100 KTS. 4 DIFFERENT CTL INSTRUCTIONS WERE ISSUED TO BOTH OF THESE ACFT. SECONDS AFTER THESE INSTRUCTIONS THE C/A SYS WAS ACTIVATED. EVASIVE ACTION WAS NOT REQUIRED AND LOSS OF ATC SEP NEVER OCCURRED. IT IS NOT UNCOMMON FOR ACFT FLYING THROUGH AREAS OF WX TO MAKE SLIGHT DEVIATIONS FROM PRESENT HDG AND AIRSPD W/O ATC APPROVAL. PLT'S MUST BE MADE AWARE THAT EVEN THOUGH A DEVIATION MIGHT SEEM SLIGHT IT COULD HAVE DRASTIC CONSEQUENCES.