What is the weight in kilograms of the player with the highest number of goal differential of all time?
weight in kilograms refers to weight_in_kg; highest number of goal differential of all time refers to MAX(PLUSMINUS);
SELECT T3.weight_in_kg FROM SeasonStatus AS T1 INNER JOIN PlayerInfo AS T2 ON T1.ELITEID = T2.ELITEID INNER JOIN weight_info AS T3 ON T2.weight = T3.weight_id ORDER BY T1.PLUSMINUS DESC LIMIT 1