Thanks for opening THIS little can-o-worms Marcello !
I can see this turning in my project du jour
While trying to figure out just what 150 mm artillery piece the Chinese could have had in the mid 30's I came across an article that mentioned the range of the German sFH 18 was less than the Russian 122 so I checked and yes indeed the 122 out ranges the German gun in the OOB's but only by a margin of 210 - 209. The article in question said it was closer to nearly 7 km
I pulled out Hoggs book and the range we have is the max range of the sFH 18 using a rocket assisted shell ( 19,000 metres )or 209 in the OOB ) the rocket assisted shell was not a standard item and could only be fired by guns fitted with muzzle breaks
The maximum range a sFH 18 could fire was charge 8 giving it a range of 13,250 m. That's 203 in game terms which fits the comment of the first article regarding it's disadvantage at counterbattery against the Russian 122.
Don