The KK of the current Legion is dead, but was a version of classic KK (current Legion is supposed to be a continuation of the original, but it has some stuff altered, so I kinda count it as a half-reboot), who, well, we all know what classic does.
Then the Threeboot one was the most recent one before that, and is the most recent living one. Fight with Ultraboy, shatter hundreds of feet of ice with a punch, all that fun stuff. Here's a scan of him making the back of an armored superhuman alien explode with a punch, these things have been fighting and threatening even the powerful Legionnaires and definitely had multi-ton strength. That was the last one of about 20 he'd defeated.
