For a critical review of the decision-making behind the surge, see this piece. I find it interesting, but am not entirely sold because the military is seen as far more unitary than probably is the case. Much of the military is not too enthused with: Afghanistan, McChrystal, Petraeus, and counter-insurgency. So, my guess is that there was pressure to lower the numbers by key parts of the military itself to lower the stress and the expense.
I do think numbers matter in ways more than just killing people. There are changes already happening on the ground as the US reinforcements from the previous decision are making it possible to do more in and near Kandahar.
Again, success depends on the politics, and if this article is right about how far apart the top US civilian and military leaders are, then the mission is in deep trouble.