Bulldozer already has a slight edge against Sandy Bridge in DX11 games, contrary to popular belief, it absolutely does. The problem is their Dr. Jeckel and Mr. Hyde nature, they have been known as we all know to fall flat on their face in DX9&10 games.
If AMD can work out those issues, and some of them do go beyond my technical knowledge, and couple that with good pricing, yes it could be.
Power efficiency is another thing, a lot of people talk about it, utilities is covered in my rental agreement, I don't much care about how much juice my computer uses. Not everyone is that fortunate however.
Don't hold your breat on FX-4320 being competitive with i5s. They aren't even meant to be, FX-4100s were meant to compete at their release date at the $130 price point down with i3s... I doubt the PileDriver x4 will be any different.