Chalk or slides for a job interview?

I think you lay it out just fine in your pro/con arguments. At the end, it is also a cultural thing: In pure math, for example, chalk talks are acceptable and not entirely uncommon. On the other hand, in applied math they are very uncommon and it would be rather surprising to see someone give a chalk talk -- to the point where people would wonder whether that is the person we would want to hire. I suspect that in other fields, that stigma is even stronger: Imagine someone in a business school giving a chalk talk.

So it depends a bit on the cultural norms in your field. I would think that a slide talk makes sure you're always on the right side. I will also point out that chalk talks have real issues with visuals. For example, if your hand writing is not extraordinary, some people may not be able to read what you have to say. Secondly, there is the saying that a picture is as good as a thousand words -- but good pictures are just really hard to do on the board because (i) it is inherently 2d, and (ii) there is a limit to the complexity that you can reproduce on a board. If there is anything in your talk that could be presented in a visual way (and I would say that there is, even though I know nothing about your research area), then it's worth doing that in a visual way and that implies that you'd be better off with slides in most cases.

I am in favor of a chalk talk when you want to present a full proof with all details (sometimes it is possible within an hour or even 30 minutes) since it often requires interacting with the audience and improvising a bit here and there depending on the questions asked. On the other hand, if you make an expository talk with some references, history, etc., slides would do nicer in general. Several more points:

a) At least in pure mathematics the black suit is not a must on an interview.

b) You may want to bring your own low dust chalk and use chalk holder to eliminate all problems with the clothes.

c) You can go slowly with slides. I usually limit my presentations to 12-15 slides per hour (6-7 for 25 minutes) counting an "unfolding slide sequence" where lines appear one after another as you say them as one slide.

d) Slides are there to catch important points in big print, not to fill a full page with long text or cumbersome computations. 10 lines per slide should be about the maximum if you want people to absorb the information. Full sentences are not required on slides: you can just say them in most cases.

e) Look at the room before starting. You may want to adopt a mixed technique using both slides and the chalkboard (just don't flip the lights on and off too often). Also, if you use slides, make sure everything works at least 15 minutes prior to the lecture (preferably much earlier than that). I've seen too many talks at which the first 10 minutes were spent on fiddling with the equipment after which the speaker had no time to finish properly or had to rush.

f) If you use slides, you may consider including some nice non-mathematical pictures in the beginning, the end, or even in the middle to make people smile and wake up. Just exercise some common sense and taste when choosing them.

g) It is quite customary to end with a "Thank you!" slide too.