Folks, just a word of warning from some details I've been keeping of my games in pref MM tier 8 tanks.
If you buy these because of the preferential MM, you are going to be disappointed.
I have played 145 games in mine:
T-34-3: 38 games (top tier twice)
112: 32 games (top tier 3 times)
Super Pershing: 55 games (top tier 6 times)
Mutant: 20 games (top tier once)
In these games, I saw tier 9 in approximately 80% of them, with the rest being full tier 8 games. You almost never get to see tier 6, ever. And when you do, you'll see bulk KV2's so your armour means nothing.
Not saying you should buy tanks to beat up on lower tiers, but if you buy a pref MM tank to have an easier time, you'll likely be disappointed.