Your Premium tanks will now bring you the following additional extra advantages:
50% bonus to crew experience. If the possibility of training your whole regiment of crewmen on one tank was not enough for you, you can now progress much faster.
Increased coefficient of battle experience depending on tier. In short – the lower the tier of the vehicle, the higher battle experience you get!
Please bear in mind that:
The Battle experience bonus does not affect the average experience of the tank e.g. for the Hall of Fame.
In the battle results window, the battle experience bonus will be displayed in a separate row, as if it were a mission.
Below is a table that shows the exact changes on each of the vehicle tiers:
TIER COMBAT XP MULITPLIER CREW XP MULTIPLIER
II 1.7 1.5
III 1.6 1.5
IV 1.5 1.5
V 1.4 1.5
VI 1.3 1.5
VII 1.2 1.5
VIII 1.1 1.5
X 1.05 1.5
These changes will be introduced with micro patch 9.2.3 on 12 September.
http://worldoftanks.eu/en/news/pc-browser/46/premium-vehicle-improvements/