Well, you really have to play well in premium vehicles in order to get good RP gain, but with a T4 premium tank, if you're good, you can unlock a T2 vehicle in one game, especially if it's the first win of the day (and/or if you have premium account).
Right now, as I said earlier, I'm back at playing WoT, and I think I have found my two new favourites: The Sherman III at tier 5 and the Charioteer at tier 8. Especially the Charioteer. Man, what a gun. You can just tear through enemy teams if you are half decent laughing, even though viewrange is a bit lacking. But apart from that, it's a beast. An absolute mondter of a TD.
Checked your builds, I like them both, though I prefer the VK.
There is no kill like overkill.