SMA PLT PERFORMS A TKOF PROC EXCEEDING THE ACFT ALLOWABLE GROSS WT.

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I USUALLY FLY AT A FLYING SCHOOL WHICH OPERATES SMA'S WHICH HAVE BEEN RETROFITTED WITH 180 HP ENGS. THESE INCLUDE A; B; AND C MODELS; BUT WE USE THE X MODEL HANDBOOK BECAUSE OF THEIR . ON THE DATE MENTIONED; I RENTED AN SMA FROM ANOTHER FBO. I USED THE X HANDBOOK TO CALCULATE THE WT AND BAL FOR MYSELF; FULL FUEL; AND 3 PAX. THE GTOW WAS 2530; 30 POUNDS UNDER GROSS WT FOR THE X MODEL. ON THE FLT FROM PRC-SEZ; I NOTICED THAT ACFT PERFORMANCE WAS 'UNUSUAL.' MAX RATE OF CLB WAS 200 FPM. I FIGURED THAT THIS WAS DUE TO THE LOWER HORSEPWR ENG AND DENSITY ALT. ON FINAL APCH TO SEZ (LOCATED ON A MESA); WITH FULL PWR AND 30 DEGS FLAPS; MIN DSCNT RATE WAS BOUT -200 FPM. DUE TO STRONG DOWNDRAFTS. PERFORMANCE ON THE RETURN LEG WAS BETTER. A COUPLE DAYS AGO; I FOUND AN OLD MODEL BOOK I HAD USED WHILE RENTING ACFT IN CANADA. I WANTED TO TRANSFER THE ACFT I RENTED MOST OFTEN (WT AND MOMENT) IN THE 'X' MODEL BOOK; WHICH WAS IN MUCH BETTER SHAPE. A COMPARISON OF THE MAX GROSS TKOF WT OF BOTH ACFT CAUGHT MY ATTN. THE MAX GROSS TKOF WT OF AN 'A' MODEL IS 2300 POUNDS. I NOW ESTIMATE THAT AT TKOF; THE ACFT WAS APPROX 220 POUNDS OVER MAX GROSS TKOF WT. A LESSON HAS BEEN LEARNED. IT IS NOW MY HABIT TO CHK THE ACFT POH (UNDER WT AND BAL) TO VERIFY THE MAX GROSS TKOF WT PRIOR TO FLYING AN UNFAMILIAR AIRPLANE; EVEN IF IT IS OF THE SAME TYPE.