SMA PLT DSNDS THROUGH A HOLE THEN CLBS ON TOP THROUGH CLOUDS.

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I PLANNED TO FLY FROM ARR TO FLD FOR THE OSHKOSH AIR SHOW. SINCE IMC PREVAILED THERE I WAS GIVEN AN X30 AM LNDG TIME AND FILED AN IFR FLT PLAN. THIS WOULD HAVE BEEN ABOUT A 45 MIN FLT. MY EXPERIENCE WITH FAA BRIEFERS IS THAT THE CONDITIONS ARE USUALLY GROSSLY OVERSTATED. THEY SEEM TO BE LIKE THE LITTLE BABY WHO CRIED WOLF TOO OFTEN. THEY ARE USUALLY NOT TO BE BELIEVED. SINCE IT WAS ABOUT EARLY AM WITH A SCATTERED CEILING AT ARR; I ELECTED TO TKOF VFR AND PROCEED VFR ON TOP AT REDUCED CRUISE SPD AND ACTIVATE MY IFR PLAN IN THE AIR IF IT WAS NEEDED. ABOUT 20 MI S OF BAE VOR IT WAS APPARENT I NEEDED TO ACTIVATE THE IFR PLAN FOR DSCNT AND APCH TO FLD. HOWEVER; CHICAGO CENTER; THROUGH THE MILWAUKEE RCO; WOULD NOT APPROVE CLRNC OF MY PREVIOUSLY FILED IFR PLAN FROM VFR ON TOP. I HAD UNDERSTOOD THE FAA PUBLISHED NOTAM FOR THE OSHKOSH SHOW TO MEAN NO IFR PLANE WOULD BE FILED FROM VFR ON TOP; NOT THAT NO CLRNCS WOULD BE ISSUED ON PREVIOUSLY FILED IFR PLANS. WITH IT NOW IMPOSSIBLE TO CONTINUE IFR TO FLD; I ELECTED TO PROCEED THROUGH A HOLE IN THE CLOUDS TO BELOW THE CEILING AND THEN VFR TO FLD. THE CTLR HAD NO OBJECTION TO THIS IDEA. HOWEVER; WHEN I REACHED THE BOTTOM OF THE HOLE AND WAS BELOW THE CEILING; THE CEILING WAS RAGGED AND ABOUT 800 FT AGL; TOO LOW TO SAFELY CONTINUE TO FLD OR FIND A LCL ARPT TO LAND. THE HOLE I CAME DOWN THROUGH WAS NOW LOST AS WELL. MY ONLY SAFE COURSE WAS TO CLB OUT THROUGH THE CLOUD LAYER TO VFR ON TOP CONDITIONS. I DID THIS ON A W HDG TO GET AWAY FROM V127. AFTER BACK IN VFR ON TOP CONDITIONS; I PROCEEDED TO PIA AND OBTAINED AN IFR CLRNC TO LAND THERE. THERE APPARENTLY ARE A COMBINATION OF FACTORS THAT LEAD TO THIS MISTAKE. FIRST IS MY EXPERIENCE WITH FAA BRIEFERS; THAT THEY CANNOT BE BELIEVED MOST OF THE TIME. SECOND WAS MY IMPATIENCE TO GET TO THE OSHKOSH SHOW. THIRD WAS THE UNCLR FAA NOTAM ABOUT VFR ON TOP TO IFR CLRNC. AND FOURTH WAS THE ACTUAL CLB THROUGH IMC TO VFR ON TOP. ALTHOUGH AGAINST REGS; THIS WAS THE SAFEST COURSE OF ACTION IN THIS SITUATION.