Football Outsiders does not release what would be considered traditional NFL power rankings. They are numbers-oriented so any rankings they provide are based more on their various proprietary statistics. They use DVOA as one of their primary tools for measuring the performance of teams and assessing where they stand in relation to each other.
Through six weeks, Football Outsiders' DVOA ratings rank the San Francisco 49ers second and the Oakland Raiders ninth. The 49ers rating benefits from a strong schedule thus far, a number one ranked special teams unit and a third ranked defense. The Raiders benefit from a fifth ranked offense and a sixth ranked special teams unit.
For the 49ers, the rest of their schedule takes a hit as they get five NFC West games mixed into their final ten games. They also face the Ravens and Steelers, but they have enough teams lower down that even if they continue to win, their DVOA will drop a little bit.
For the Raiders, the question is how their offense will hold up in light of the injury to Jason Campbell and their trade for Carson Palmer. Although Darren McFadden is considered the engine of this offense, they are actually balanced in the eyes of DVOA with a seventh ranked pass offense and sixth ranked rush offense. It remains to be seen how Palmer impacts the offense, so we'll just have to wait and see over the coming weeks.