On all the lens charts it shows the 200mm step as being very very high in IQ the same as most Pro level 200mm f2.8 lenses costing thousands, and the 300mm being ok and usable just not in the same league as at 200mm.
P.
I have tried some shots at 135mm and they look superb, admit they were of planes a lot closer, but i could see the difference between 300mm and sub 200mm, miles different.
P.