I disagree that your clock doesn't start until you finish the PhD. I think your clock starts when you start the PhD. If someone takes 7 years to graduate, their 5 pubs in grad school won't look as good as the person who took 4 years to graduate and has 4 pubs in grad school.
And while I agree that it's good to use the extra time to get more papers "in the hopper," I think that most people have more trouble landing a job than they do have trouble getting tenure once landed. In fact, given the competitiveness of the job market, I'd propose that the tenure standards at any given school are relatively lax compared to the hiring standards at that same school. So if you're planning on applying in the fall, get papers out NOW. That said, once you know your submissions will be too late for job applications, you might as well sit on them and collect data to have a bunch of things ready to go out when you're going to start your new position, giving you a head start on tenure. But keep in mind that at most places, they'll expect some (much?) of your portfolio to come from work that you started at the new place and/or for which you are the PI (not just first author, but senior author.)
All of this said, to answer your first question, I think that for most people staying an extra year is beneficial. Usually you've hit your stride and you can get a lot done relatively speaking in that final year - probably more so than you could in a postdoc in which you'd be starting somewhere fresh. I often think I should have done a 6th year instead of taking a postdoc myself! My only word of caution is that some places don't like applicants who are still in graduate school, I guess because they are concerned the applicant won't finish? In that sense, it is helpful to apply with a PhD in hand.