When I ran the CC adventure path, we took around 1.75 years to finish. We played in weekly 4-6 hour sessions, with a big push at the end of 8 hours Sat-Sun a few weeks.
A Serpent Skull game I play in with mostly the same group has been going on for closing on 3 years now, but play time was closer to 2.5 hours a week for over a year there, which was too short to really get much done. Lately its been 3-4 hours a week, with occasional 8 hour extra session.
For session speed, I'd limit yourself to 4 players. Even 1 extra player makes a big difference in how long combat takes at higher levels. Having players preroll attacks and damage also helps a lot.
For GM prep time, I found Herolab a huge time saver for mid to high level enemies, for quickly defining monster feats, spells, abilities.