I just got back from the dealer and decided that when I finally buy one it will be with the 8th seat. I measured the middle seats with the 8th seat installed and found it to be roughly 51". Our Camry is about 54". Both have about 10" between the belts in the middle. For me there were a couple of determining factors. The sunroof is very cool, but even within the test drive time the novelty wore off for my wife and myself. We have 2 cars with sunroofs and almost never use them, but the Pacifica sunroof is very nice. If you are a true sunroof person I can see how the sunroof might win out.
So, for me the 8th passenger might be a little cramped, but it would beat taking 2 cars. The real deciding factor though was when I measured the back (3rd row) seat. The width of the back seat is only 46" with 8" between the belts. That could be really cramped for adults. When I have 5: it will be 2-2-1, for 6: 2-2-2, but when I have 7: it will be 2-3-2 (and of course 8: 2-3-3). The back seat (like on all mini vans is really narrow for 3 adults.