~40FPS is fine, really.
Yea, considering the cost to get a few FPS more.
OCing with Afterburner is pretty easy, I myself use it. BUT OCing a GPU is a tad bit riskier than a CPU. If a CPU OC fails, the PC crashes and it resets. If a GPU OC fails, it fails pretty bad. Nothing to discourage you from doing it though. Look around to see how much others get on your exact same card before going in.