Thanks.

Any photos taken with it?

As with all these things there's pluses and minuses. I guess tethering is always going to be a hassle on location whichever system you opt for so it depends how essential tethering is. The K-1 has a great optical viewfinder so I would never consider lugging PCs and things to basically do the same job. If tethering is essential for what you do and you don't use the optical viewfinder is Pentax the way forward? You might be better off with a mirrorless, eg Sony Alpha. Don't though ask me what that would be like for tethering as I haven't a clue!

Given the field of view I'd expect the filter system would have to be extremely huge! One's quite likely to include one's feet accidentally so filters might have to reach to one's shoes! Apparently there's a slot at the rear for gelatine filters. Most grad effects can be done in PP anyhow aided by the dynamic range of current cameras provided the image was taken raw.

There's a review on Youtube here (not the Pentax version.) Seems pretty good.

Why do you actually want to upgrade it if it's all working for you with what you have? I could understand if you'd seen something else that tickled your fancy and you're checking compatibility etc. but that doesn't seem to be the case. Keep the working setup you have for your jewellery shoots and get something newer for other things where tethering isn't an issue.
Then having got something else you could test it out to see if it would do a better job than the K-5. It might not!

The hand would have been periodically static as the stair were climbed. The exposure I'd guess would be around a second a step, thus about 7 seconds. The hand may have been in one spot long enough to register. Certainly an interesting experiment.

Ilford Pan F at ISO50 is finer grained than FP4 and HP5, but really you need the right film for the job in hand. You can't realistically change the rating halfway through a film. One could take a part used film out and change it and put the other one back later. I have done that though did lead to some double exposures not quite remembering how many shots had been exposed.
FP4 is a good general use film, with HP5 the grain becomes more obvious.
My Dad used to like using Pan F under exposing it by a stop and compensating in development almost all the time. I normally preferred FP4 as it was more forgiving with regard to latitude in exposure and could use the times given with the chemicals.
When it comes to exposing B&W negative film, expose for the shadows.

Two bunches of bananas. Where was it picked up, a charity shop?

It would be interesting to see reviews of the older K and M lenses where the tests compare to those used for recent lenses. I might be able to help where I could bring some over when I stay over on your side and perhaps you could bring them back on a visit to this side. They'd all be K mount. See what others can offer though as a local source would be easiest.
What does it entail making an Imatest?
I suspect with older optics some will have had a harder life or been stored badly so results between samples could vary quite a bit.