A LEAR 35 EXPERIENCED AN ALTDEV WHEN TRYING TO TOP HVY WX.

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CTR ADVISED US OF A LINE OF TSTM ACTIVITY AHEAD THAT WOULD BE IN CONFLICT WITH OUR CURRENT FLT PATH. ADDITIONALLY; WE WERE GIVEN CLRNC TO DIVERT AS REQUIRED. THIS RPT WAS BACKED BY OUR RADAR. AT THE TIME WE WERE VMC AND COULD SEE THE LINE AND THE TOPS. THERE WAS A CLR PATH TO THE S WHICH WOULD NOT REQUIRE A CHANGE IN ALT AND WOULD ADD 10 MINS TO THE TRIP. FUEL WAS NOT A FACTOR. IN LOOKING AT THE RADAR; MY ADVICE TO THE CAPT WAS TO GO S; AND THE TOPS WERE HIGHER THAN THE ACFT'S SVC CEILING OF FL450. THE PIC SAID; 'THE RADAR MAY NOT BE CORRECT AND IT LOOKS LIKE WE CAN CLB OVER IT.' AS WE CONTINUED; WE PUT FL410 ON REQUEST AND BECAUSE WE WERE THE ONLY ACFT ATTEMPTING TO FLY OVER THE SYS; WE WERE GIVEN FL410. AS WE STARTED XING THE TOP; TURB PICKED UP AND WE WERE BECOMING IMC. WE REQUESTED FL450 -- AGAIN CLRED TO CLB. AT FL450 WE HIT SEVERE TURB; STILL IMC. THE ACFT WAS PUSHED 2000 FT UP TO FL470; THE AUTOPLT KICKED OFF AND THE ACFT ROLLED 30 DEGS TO THE R. THE IAS FELL OFF AND ANGLE OF ATTACK INCREASED TOWARDS STICK SHAKER. I INCREASED THE THROTTLES SLOWLY TO PREVENT FLAMEOUT OR A STALL. SHORTLY AFTER THAT; THE ACFT CAME BACK TO VMC AND WE DSNDED BACK TO FL450. WHILE AT FL470; THE PIC REQUESTED FL470; WHICH WAS GIVEN TO US. AFTER THE EVENT; THE PIC TOLD ME THAT THE REASON WHY HE WANTED TO GO OVER THE TOP WAS TO SHOW ME WHAT THE LEAR 35 COULD DO.