ACR X NON ADHERENCE TO ATC CLRNC. MADE TURN EARLY.

Narrative

ACR X (DC9-40 CREW) WAS GIVEN POS AND HOLD AWAITING TKOF RWY 25R AT LAS BEHIND A B727. AS THE B727 ROTATED AND CLBED OUT; WE WERE CLRED FOR TKOF. WE WERE CLRED THE MEAD 9 DEP WHICH CALLS FOR A R TURN FROM RWY HDG TO 070 DEGS AT 4000 FT OR 4 DME; WHICHEVER OCCURS FIRST. OUR TKOF WT WAS LOW AND WE REACHED 4000 FT AT APPROX 2.5 DME AND BEGAN OUR R TURN TO 070 DEGS. SHORTLY INTO OUR TURN; WE'RE TOLD TO LEVEL OFF AT 5000 FT (WE HAD PREVIOUSLY BEEN CLRED TO 7000 FT) AND GIVE A MAX RATE TURN TO OUR HDG. IT WAS MOMENTS LATER WE LEARNED WE WERE TURNING INSIDE AND CLBING MUCH FASTER THAN THE B727 THAT HAD DEPARTED AHEAD OF US; AND THAT WE SHOULDN'T HAVE BEGUN OUR TURN UNTIL 4 DME. WHEN THE CAPT AND I DISCUSSED THIS; WE FOUND CLRNC DELIVERY HAD AMENDED THE MEAD 9 TO TURN AT 4 DME. AS THE CAPT HAD RECEIVED THE CLRNC AND I; THE PF; HAD NOT COMMUNICATED THIS CHANGE VERY WELL ON THE TKOF BRIEFING; THIS ERROR OCCURRED. IMMEDIATELY AFTER RECEIVING THE CLRNC WE WERE GIVEN A 40 MIN GATE HOLD AND ALSO INFORMED THAT INTENDED DEST HAD GONE BELOW MINIMUMS. THIS DIVERTED OUR ATTN TO NOTIFYING COMPANY OF DELAY; POSSIBLE CHANGE IN FUEL LOAD; NEW WX; ETC. AFTER A CLOSER LOOK AT THE MEAD 9; WE FOUND THE 4 DME TURN; IN LIEU OF THE 4 DME OR 4000 FT; WHICHEVER OCCURS FIRST; IS THE NORM; RATHER THAN THE EXCEPTION. THE REASON BEING THE DIFFERING LEVEL OF TURBOJET PERFORMANCE DOESN'T ALLOW PROPER SEPARATION; WHICH CALLS FOR A MORE DEFINED POINT TO START THE TURN. WE FEEL THE MEAD 9 SHOULD BE CHANGED TO REFLECT THIS AND PREVENT FURTHER PROBS OF THIS NATURE.