LGT UNABLE TO COMPLY WITH CLB RESTRICTION AT ALT.

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FLT ORD-RDU ON MAR/XX/94 DEPARTED AT XA25 LCL WITH A LIGHT LOAD. NORMALLY; ATC KEEPS YOU AT FL290 UNTIL ALMOST S OF INDIANAPOLIS (VHP); AND THEN WE ARE CLRED TO CLB TO FL370. ON THIS TRIP WE WERE ASKED IF WE COULD BE LEVEL AT 37000 FT WITHIN 5 1/2 MINS. WE CHKED OUR PERFORMANCE COMPUTER; WHICH INDICATED 5 MINS TO FL370 AT THIS PARTICULAR WT; SO WE ACCEPTED THE CLRNC AND PROCEEDED TO CLB. IN SHORT; THE PLANE RAN OUT OF STEAM AT 36000 FT AND REFUSED TO CLB FURTHER WITHOUT GETTING LOW SPD WARNINGS. WE REQUESTED RELIEF FROM THE CLB RESTRICTION (5 1/2 MINS) AND DSNDED TO FL350 TO REGAIN SPD. THERE WAS NO CONFLICT INVOLVED (I ASKED); BUT I AM WRITING BECAUSE I BELIEVE THE PERFORMANCE INFORMATION CONTAINED IN THE PERFORMANCE MGMNT SYS OF SUPER 80'S IS OVERLY OPTIMISTIC AND CAN LEAD TO PROBS WHEN ACCEPTING 'TIME TO CLB' CLRNCS (SOMETHING I WILL NEVER DO AGAIN). ALSO; I BELIEVE THE ATC CLRNC WAS GIVEN TO PROVIDE RELIEF FROM SECTOR CRITERIA BTWN ATC FACILITIES; NOT BECAUSE OF ACTUAL TFC AVOIDANCE. JUST BECAUSE A LOA EXISTS BTWN SECTORS TO HDOF ACFT AT CERTAIN ALTS DOES NOT MEAN MY FLT HAS TO BE BURDENED WITH A CLB RESTRICTION IN TERMS OF TIME. A DISTANCE RESTRICTION WOULD BE BETTER IN THE FUTURE. FOR YOUR FILES; I HAVE WRITTEN THIS UP.