LESS THAN STANDARD SEPARATION BETWEEN CORP JET AND COMMUTER ACFT. OPERATIONAL ERROR.

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CORP X WAS INBOUND TO LUK ON V128. ACFT X WAS KEPT HIGH (FL240) DUE TO NUMEROUS DEP ACFT EBOUND ON V128 (HEAD-ON)-ONCE CLEAR OF THESE EBOUND JETS ACFT X WAS DESCENDED AND TURNED LEFT FOR FL130 TFC LNDG DAY FROM OVER FLM ON THE BUCKE 2 ARR. RESTR AREA R5503 WAS HOT AND IN USE SO CORP X COULD NOT BE TURNED TO THE RIGHT - THIS ACTION PUT A FASTER ACFT X BEHIND A SLOWER COMMUTER ACFT Y WAS ALSO EXTRA SLOW SINCE THE WINDS WERE OUT OF THE NE AND RIGHT IN IN IT'S FACE. ACFT X WAS ASKED TO TURN FURTHER LEFT AND INCREASE IT'S RATE OF DESCENT THROUGH FL120 CONFLICT ALERT ACTIVATED AND X REPORTED OUT OF FL125 AT THE SAME TIME WITH A LOSS OF SEPARATION - 4.2 MILES. I WAS NOT TALKING TO Y SO WAS UNABLE TO TURN THAT ACFT UNTIL CONFLICT ALERT ACTIVATED; I THOUGHT THAT I WAS GOING TO HAVE 5 MILES AND ALSO 1000' - BUT I WAS WORKING ON THE 75 MILE RANGE AT THE SECTOR WHICH IS NORMALLY WORKED ON 100 MILE RANGE. 5 MILES IS A LOT BIGGER THAN ON THE 75 MILE RANGE - THE ONLY REASON THAT I CAN THINK OF WHY I WAS ON THE 75 MILE RANGE IS BECAUSE I HAD BEEN WORKING ON THE 75 MILE RANGE FOR THE PAST FEW WEEKS WHILE TRAINING ON MY ADDITIONAL SECTOR. A LOT OF THINGS COULD HAVE BEEN DONE (LOOKING BACK) TO NOT ALLOW THIS SITUATION TO DEVELOP; A GREATER TURN; A 360; A DIFFERENT ROUTING - OVER FCM DIRECT LUK FOR CORP X INSTEAD OF HEAD ON WITH ALL THE EBOUND DEPARTING JETS OFF CVG; I WAS ALSO BUSY WITH 10 OR MORE OTHER ACFT ON THE FREQ; HALF OF WHICH WERE ON VECTORS (MOSTLY AROUND THE RESTR AREA) WHO I WAS NOT AWARE OF SINCE THE MANUAL CTLR TOOK A FEW HANDOFFS FROM HTS APCH (WHICH IS A NON-ARTS FACILITY SO THE R-PERSON MUST START A TRACK) AND DID NOT TELL ME WHICH COST A FEW VALUABLE SECONDS.