CL65 AT FL350; WITH ZMP; REQUESTED FL410. AT FL410; EXPERIENCED BUFFETING AND REQUIRED EMER DSCNT.

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WE WERE CRUISING AT OUR FLT PLANNED ALT OF FL370; AND DECIDED TO CLB TO FL410. WE CONSULTED OUR STEP CLB CHARTS. SINCE OUTSIDE AIR TEMP WAS ISA -5 DEG C; AND OUR INITIAL CLB WT WAS 40700 LBS; WE DECIDED WE COULD MAINTAIN A CLB RATE OF ROUGHLY 110 FPM AT FL410. WE RECEIVED CLRNC TO FL410; SELECTED CLB THRUST IN THE FMS AND WERE ABLE TO CLB TO FL410 AT 500 FPM. WE LEVELED OFF AT MACH .68-.69; BUT CONTINUED TO LOSE AIRSPD. WE REQUESTED A LOWER ALT AND WERE TOLD BY ZMP THAT IT WOULD BE ANOTHER 5 MINS DUE TO TFC. WE NOTICED TFC AT FL390 ON THE TCASII DISPLAY. APPROX 15 KTS ABOVE THE LOW SPD STALL AWARENESS RASTER; WE NOTICED SLIGHT BUFFETING AND REQUESTED A HDG SO WE COULD DSND AWAY FROM TFC. ATC TOLD US TO TURN R 20 DEGS. AT THAT POINT; THE AUTOPLT DISCONNECTED WITH THE STICK SHAKER AS WE WERE MAKING THE TURN. I IMMEDIATELY NOTIFIED ATC THAT WE COULD NOT MAINTAIN ALT AND THAT WE NEEDED TO DSND NOW. ATC STATED THAT; 'IF YOU WANT TO DSND NOW; YOU MUST DECLARE AN EMER.' WE RECEIVED A TCASII TA AS WE WERE DSNDING. WE HAD THE TFC IN SIGHT AND LEVELED OFF AT FL397. ATC THEN ASKED WHAT ALT WE WANTED; AND WE TOLD THEM FL370. ATC THEN CLRED US TO FL370 AND DIRECT DEST. AFTER REVIEWING THE FLT SEQUENCE OF EVENTS SEVERAL TIMES ON MY OWN; I BELIEVE WHAT CONTRIBUTED TO THIS INCIDENT WAS THE FLC'S INACCURATE INTERP OF THE CL65 STEP CLB CHARTS AND FAILURE TO FOLLOW THE PROFILE SPELLED OUT IN THE STEP CLB CHARTS.