I have played A Zildjians since I started playing, so I know them well. I recently wanted to branch out into another sound, and thought K's might be the way to go, but I have not found anything that really makes me feel like: "This is a sound I want".
It always starts with the 'key' cymbal, and for me that is the 16" thin crash. from that first crash cymbal, I have built up a collection that works well with that cymbal for me.
Once I find that "key" cymbal in another line (MAYBE K Constantinople line??) I can then start to build another set- sort of like moving onto a new painting after finally putting the last strokes on a painting that has been a few decades in the making. I think I am so entrenched in "my" sound, that I am having difficulty moving on, but that is what I feel I must do.
Don't get me wrong though, I can select a few cymbals from my collection and be prepared for any gig from brush work with a piano duet to a head banger's ball. And I have most of my collection set up on my main kit all the time because they all have a place in different dynamic levels of various musical styles. I guess growing up listening to Buddy Rich also cemented my internal 'reference' as Zildjian A's- to me, they sound like good cymbals should.
Now, I do have a couple 'duds' in my collection as well. Those are some of the heaviest cymbals I own as well. I have an old 22" ride that is just crazy and also a 19" med crash that really needs it to be LOUD to get away with using- it might be a better left side ride than a crash in fact. I did use both of those (along with my 15" field cymbal high hats) in a "Bonham" kit for a while- 15" ride tom, 18" floor tom and 22X14 bass. I used my Luxor snare with that too, and I have to say that the washy, ringy, almost 'sloppy' sound of those drums with those cymbals really gelled well. Needless to say, it was a thunderously loud kit, and part of the reason those massive cymbals fit so well.
My experience has been that the Z line is a bit heavier and more focused due to lack of lathing on a lot of the models. I like the more complex overtones of the A line, and this may be why the K line is not exciting me at the moment either- they have a 'niche' where they fit, and my style of play (historically) has been more diverse. My private lessons were predominantly jazz, while my listening taste was Zeppelin, Rush, Yes and other heavier bands growing up. (now my music collection is all over the map from Lords of Acid to Dave Brubeck to Steely Dan to Fishbone...)
I think I, like you, need a cymbal 'loan' as you put it, to set up a 4-piece kit (the old Yam kit is coming along) with these loaner K cymbals and just play them for a few hours. I always like to hear K's on recordings such as Chic Corea Alive, but never seem to find 'the' sound when I'm shopping- of course the 31-band parametric can make a bad cymbal sound good and vice versa as well, so we have to keep that in mind when shopping, and another point you mentioned is that the sound of a cymbal at 18" is VERY different than the sound at 18' or more- Field cymbals are a good example of that, because you feel like you are clanging a pair of un-rolled ingots together but 20 yards away, they sound pretty nice!
Still searching...