When it comes to winrates at the microlimits, over 10PTBB is sustainable and that to be killing the game you would be beating it for more than that. At the higher limits 8 would be absolutely destroying the game and is not sustainable.
Agree, but +8ptbb/100 winrate is certainly sustainable, you just have to be crushing the game.

Btw, at 2+2, the general consensus is that +5ptbb/100 is killing a game. Take that for what it's worth...