Overall, I've had good results with PyrocatHD for mixed-use negatives not terribly inclined to change
It if works, it works! I don't have experience with FP4+ for this particular purpose in the way you develop it. When I frequently did salted paper, I used to develop for about twice as long as recommended for normal development. Pyrocat 1+1+100 at 14 minutes for this film sounds on the short side to me, but you've got the negatives and I don't!
Hmmm, I have that same Everbeam LED as recommended by Sandy King.
The problem with many of those fixtures sold on eBay, Amazon, AliExpress etc. is their overly optimistic power ratings. To give an example: very recently I picked up an array of 365nm + 400nm dual wavelength floodlights from AliExpress. They're advertised as "300W" units. I knew from earlier experience with an identical unit at only 400nm wavelength that the true power dissipation of the unit was only 75W - so 75% less than advertised. When I received the dual wavelength units last week and put them to the test, I arrived at a real power rating of only 32W. A further complication was that the fixture included a transparent plastic faceplate & lens assembly. This material blocks virtually all 365nm light, further reducing its actual efficiency.
This is all to say that comparing LED fixtures is tricky. Comparing the fixture I wrote about to my home-built 100W (actual, real-life Watts) exposure unit, of course the comparison was totally out of whack.
A further complication is that 365nm LEDs are currently still far less efficient than 400nm LEDs. For processes that are sensitive across a broad bandwidth (e.g. Van Dyke, Kallitype) a 400nm LED unit will almost always compare favorably to a 365nm unit of a similar power rating.
I don't have hands-on experience with that Everbeam fixture, but if I had one, I'd definitely measure its power consumption and open the unit up to analyze its circuitry and get an impression of its actual potential. There may be good reasons why a unit sold as a 100W unit performs no better than a decently engineered and accurately rated 10W unit. But it depends on a whole slew of factors and that makes such a comparison often too difficult to understand/interpret well for the average alt. process printer.
The issue is, sadly, rather complex. The short of it is that if you get long exposures with that unit, then all I can say is that I don't doubt your observations and the fact that someone else reports much shorter exposures with another unit of the same power rating (and another process) just doesn't say much.
with your processes, long times create the possibility of variation from print to print depending on coatings and humidity.
I'm frankly not too worried about this. Salted paper works fine if dried completely. Working with silver gel negatives generally already gives some margin for variation and that tends to swamp more minor effects such as the ones you mention. When I frequently did salt, my exposures were 10-15 minutes. The only thing that really influenced them was the negative. All other parameters had marginal effects at best.
Mind you, I understand and accept that processes like Pt/Pd and a couple of others are more prone to this issue since they're often practiced at higher humidity levels that are not always sustainable during long exposures.
