40/40 is stabiliser speed.
However Sosna U/PNM-T limit it to aiming speed of 5° vertical.
And typically game tries to use aiming speed over stabiliser speed.
So aiming speed in the B3M/BVM/M is 40/5, stabiliser speed is 40/40.
40/5 is currently in internal bug report, idk when they will implement it.
For example for 2E42 stabiliser series used in T-72B, T-80U/UD the maximum vertical stabiliser speed is 8,5°, however you will never have that speed be achievable in actual tank due to stabiliser being linked with sight, which limits vertical speed to some small number.
That is aiming speed.
B3M/BVM/M use 2E58
2E58 uses different design which also allows to save energy in comparision to older models.
2E42M (russian one, the 2E42M exists in three different forms: russian, soviet, ukrainian. they do not share all specifics!) is just a modification of old 2E42 which was made in like 70s.
Hence why 2E42M doesnt increase vertical stabiliser speed anywhere as much as 2E58.
Ah, yes, something that requires much less knowledge & time (including 2E42M stabiliser due to people literally submitting it to devs) is modeled earlier and first.
Not even the end of dev server but someone has to whine IG.