A C560 CREW; TRYING TO ESCAPE STRONG HEADWINDS; REQUESTED AND RECEIVED A CLRNC TO FL430. DURING THE CLB ACFT PERFORMANCE DECLINED; A LOWER ALT WAS REQUESTED.

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WE WERE CLBING TO FL390 AFTER DEPARTING TEB. AFTER CHKING THE FLT MANUAL; WE DECIDED TO CONTINUE OUR CLB TO FL430 TO FIND AN ALT WHERE THE WINDS WERE NOT AS STRONG. WE WERE CLRED TO FL430. AS WE CLBED THE LAST 300 FT TO FL430; OUR AIRSPD BEGAN TO DECAY RAPIDLY. AT THIS TIME; WE WERE GIVEN A FREQ CHANGE TO TORONTO CTR. WE LEVELED OFF AT FL430 AND OUR AIRSPD DID NOT INCREASE AND WE BEGAN TO HEAR THE RUMBLE OF AN IMPENDING STALL. I DISCONNECTED THE AUTOPLT AND INITIATED A DSCNT TO INCREASE OUR AIRSPD. THE COPLT CHANGED RADIO FREQS AND AFTER A MOMENT OF HESITATION ABOUT WHAT TO SAY; WHEN HE CHKED IN; I KEYED THE MIKE AND TOLD THE CTLR THAT WE WERE DSNDING OUT OF FL430 FOR FL410. AFTER A MOMENT OF CONFUSION; THE CTLR CLRED US TO DSND TO FL410. I FEEL; I SHOULD HAVE MADE MYSELF MORE CLR TO THE CTLR THAT WE WERE UNABLE TO MAINTAIN FL430 AND WERE DEVIATING FROM OUR ORIGINAL CLRNC. DURING THIS OCCURRENCE; WE DEVIATED APPROX 700 FT FROM FL430 BEFORE RECEIVING A NEW CLRNC. I BELIEVE THAT HAD WE NOT INITIATED AN IMMEDIATE DSCNT; THE ACFT WOULD HAVE STALLED.