THE ACFT TOOK OFF AT 1054 CDT IN VMC WITH NO FLT PLAN. AT THAT TIME, THERE WAS A RPRTD CEILING OF 1800 FT. AT 1112 CDT, THE PLT RPRTD HE WAS AT 10,000 FT, 'JUST REACHING THE TOPS.' AT 1137 CDT, HE STATED 'WE'RE ABOUT 60 WEST OF OKE CITY, WESTBOUND TO SAYRE VOR & WE'RE AT 12,500 FT & NOT QUITE ON TOP . .' APRX 7.5 MIN LATER, THE ACFT EXPERIENCED AN IN-FLT BREAK-UP & CRASHED WHILE ON A WESTERLY HDG APRX 19 MI WSW OF THE DEPARTURE ARPT, WELL EAST OF WHERE THE PLT HAD LAST RPRTD HIMSELF. THE WRECKAGE WAS SCATTERED OVR A 4600 FT AREA ALONG ON A HDG OF 292 DEG. WITNESSES RPRTD HEARING THE ENG AT HI RPM, THEN HEARD A LOUD BANG. SHORTLY THEREAFTER, THEY SAW PIECES OF THE ACFT FALLING OUT OF THE CLDS. AN EXAM REVEALED EVIDENCE THE LEFT WING & BOTH RUDDERVATORS HAD SEPD FM OVERLOAD FAILURE. THE LAST ENTRY IN THE PLT'S LOGBOOK WAS DATED 11/1/84. HIS LAST RECORDED FLT IN A BEECH 35 WAS ON 2/2/84. AN NTSB WX STUDY SHOWED CLD BASES AT APRX 3000 FT,CLD TOPS AT 12,500 FT, LGT TO MOD RAIN & LGT TO MOD TURBC BELOW 14,000 FT. NO PRE-ACDNT MECHANICAL PROBLEMS WERE FOUND.