I think that about 750 cc (45 cu. in.) is about the biggest "performance" two stroke was ever built , that would be the Yamaha TZ750, which was a true race engine and both Suzuki and Kawasaki modified street engines to compete. A good TZ750 was good for up to around 150 hp (some could have been a bit higher) but the real "killer" two strokes were the last of the GP two stroke motors, 500 cc's and 250 hp! They had BMEPs over 300 psi! better than any four stroke has ever made. All that horsepower from an engine that had no valves and was completely dependent on the resonate frequency of the intake and exhaust tracts to make power! Very impressive motors. Would love to have one to run in a K class anything.
Rex