Yep, like I posted before, I got up to Tier 6 (7? I forgot) with the German TDs. It was easy enough with the free gold they gave out during beta, you really didn't have to worry about money, only experience. Without gold, you might unlock tanks 2 Tiers above but not have enough money to advance to it. The grind is just horrendous in this game.
I can tell you this though, if you decide to go down the German TD tree, the Marder II, and the Stug III are some of the best fun youll ever have.