I have flown around 6000 hours just in the King Air range mainly 200 and B1900. The 200 changed around serial number BB-827 moved accross to the Super Kingair B200. The difference being in the engine from PT6-41 to PT6-42 (still 850sHP). It was able to pull more horsepower at higher altitude. The pressurisation went from 6 psi to 6.6 psi as well and the ZFW increased from 10400 lbs to 11000lbs.
The King Air 300 came out as a 300LW and 300. Light Weight (LW) would take-off at 12500 LBS single crew and the the natural 300 would take-off at 14100lbs, but required two rated pilots. The only difference between the two was a placard near the door to confirm if it was an LW or not. The fuselage was the similar to the 200/B200 but it had two emergency exits, one on either side. The engines would push out derated 1050HP in both cases.
The B350 was a stretched 300, same engines and flew a little faster than the 300. This was possibly due to fuselage design being a little longer.
These are all beautiful aircraft to fly.