CAPT OF AN AIRBUS A310 OVERSHOT ASSIGNED ALT DURING GAR DUE TO GAR CLB PWR SET AND CLOSE PROX TO ASSIGNED ALT.

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NIGHT CARGO FLT CLE-IND. ARRIVING IND FROM THE NE; LNDG RWY IN USE AT IND WAS RWY 5R/L. APPROX 15 MI FROM THE ARPT AND STILL TO THE NE; THE RWY WAS CHANGED TO LAND RWY 23L/R. WE WERE AT 7000 FT MSL ON A VECTOR AND ONLY ABOUT 5 MI FROM LAREZ (OM FOR RWY 23L); WHEN APCH CTL CLRED US FOR ILS RWY 23L. XING ALT AT LAREZ OM IS APPROX 2700 FT MSL. EVEN WITH THE ACFT IN THE LNDG CONFIGN; WE CROSSED LAREZ AT AROUND 3500 FT MSL. BOTH THE CAPT AND I AGREED WE WERE TOO HIGH; WE BOTH AGREED WE DIDN'T LIKE OUR SIT; AND WE BOTH AGREED TO ABANDON THE APCH. THE CAPT THEN ACTIVATED THE TOGA LEVERS AS I WAS CALLING THE TWR TO STATE THAT WE WERE GOING AROUND. THE TWR STATED 'ROGER;' AND TOLD US TO MAINTAIN 3000 FT. WE HAD ALREADY GOTTEN TO WITHIN 3-4 MI OF THE RWY AND DOWN TO 2700 FT MSL WHEN THE TOGA LEVERS WERE ACTIVATED. WE HAD ALREADY PASSED THROUGH 3000 FT ON THE GAR WITH TOGA PWR STILL APPLIED. THE AUTOPLT AND AUTOTHROTTLES WERE THEN DISCONNECTED; THE AIRPLANE WAS IMMEDIATELY MANUALLY CTLED; BUT WE WERE NOW AT APPROX 3500 FT AND DSNDING BACK TO 3000 FT AND VISUALLY DIRECTLY OVER THE RWY. TWR RESTATED TO MAINTAIN 3000 FT; WHICH WE DID; AND WE RETURNED DOWNWIND FOR ANOTHER APCH AND UNEVENTFUL LNDG. 2 MAIN CAUSES RESULTED IN THIS SIT. 1) CHANGE IN LNDG RWY IN CLOSE; LEAVING US 'HIGH AND HOT.' 2) ACTIVATION OF TOGA CLOSE TO THE ALREADY SELECTED MISSED ALT OF 3000 FT WITH SUPERIOR ACFT PERFORMANCE; PREVENTED CAPTURED ALT LEVELOFF.