It is premature to think 8 wins for the Raiders without McNabb. If projecting ahead, look at their 2010 opponents.
Away: KC, DEN, SD, SF, ARI, JAX, TEN, PIT
Chiefs are the only team Oakland will play on the road that won fewer games than them. They will play 7 road games against teams that won at least 8 games.
Home: KC, DEN, SD, SEA, STL, MIA, HOU, IND
Admittedly softer home schedule (again, this is on paper as of right now); the Seahawks, Rams, Chiefs are 3 games against teams that were worse than Oakland. But Indy, Houston, Miami, and all of the division games will be tough.
Hard to see see how one can project them to do anything better than 2-6 or 3-5 on the road with those opponents. They would have to then win at least 5 games at home to get to 8 wins. This opinion finds it more likely to lose 5 of those home games than win 5 of them.
The Patriots are still going to get a top 12 pick at this rate, conservatively. It is a McNabb trade that could be a wild card toward getting the team to 8 or 9 wins. This opinion finds it more likely that McNabb is the starting QB for the Eagles next year.