I think cactus hit the nail on the head. In the two RIs where I've earned degrees, presenting one's writing sample as a job talk would be the kiss of death for a candidacy. The only thing I might say different relates to the following:
Finally, I was told that it is better to pick a chapter based on a text that most faculty are likely to have read (e.g., Doctor Faustus) than it is to pick something more obscure (e.g., Two Noble Kinsmen) –– even if you think your Two Noble Kinsmen chapter is better than your Doctor Faustus chapter. (Thankfully, I didn't have to worry about this since my favorite chapter is on a widely-read text.)
It's possible to give a very good job talk on texts that no-one in the audience has read provided that you're not focusing on a single text. I remember one job talk I attended on regional ghost stories. No-one had in the audience had read any of them. Perhaps more important, no-one
should have read any of them. The speaker did a fabulous job of summarizing the tales and choosing relevant quotes to illustrate points, and we all walked out feeling that we'd learned something new. What you probably want to avoid is focusing on a single text that people will feel like they should have read but haven't. cactus's example of Two Noble Kinsmen is a good one. Audience members likely will not have read it in recent memory but probably will feel like they should be familiar with it - a very awkward rhetorical situation.
As far as the level of formality in different situations, I think I'd advise you to be yourself. How would you approach an academic dean at your current institution? I'd keep that level of formality when you meet your dean. How would you talk/act when riding around in a car with faculty at your current place? That's probably a good guide for you on your city/campus tour.