This is a summary of a Russian vlogger known for his lab work:
Improved rotator4.01s vs 4.3sGun Laying Drive (Tiger I) https://youtu.be/0UNYjeK4D2s?t=179 Running max speed, stopping, measuring aim time
V Stab + Rotator5.18s vs 5:27sV Stab + Vent (Defender) Running max speed, stopping, measuring aim time https://youtu.be/0UNYjeK4D2s?t=329 V Stab + Rotator7.20s vs 7:22sV Stab + Vent (Defender) 180 deg tank rotation (both chassis and turret) + full aim (see vid) https://youtu.be/0UNYjeK4D2s?t=358
I assume 10% Rotator and 5% Vent were used, it's not clear.
Summary:
Gun Laying Drive is useless, V Stab is more practical (except some arties where Vent isn't an option).
Rotator's 10% faster turning increases the aiming circle. Additional 10% stab there is to compensate for that.
There is no noticeable difference b/w VStab + Rotator and V Stab + Vent setups. Vent gives you some extras, e.g. loading, but they mostly negligible (https://youtu.be/0UNYjeK4D2s?t=268)
The above with bonned Vent with +8.5% instead of +5% makes more sense, mostly due to the loading speedup.
While WoT UI claims VStab + Rotator gives +30% stab, that's not true. Read the disclaimer in the pop up. My calculations predict ~27%.
Credit: Barabekus on Youtube (map guides, lab tests, hints etc. but in Russian). Pls subscribe or like the vid if you find it useful.
I try to follow EQ2.0 tests. If there is interest, I'll try to translate the results I find. Hope it helps.