Ok, so I'll post my findings again as it seems like my last post wasn't sufficient. And since I spent about another hour just testing all my sliders against about every type of keycap type I have; I wanted to post more findings.
So first of all I turned my keyboard upside down to see which, if any, of my jtk keycaps would fall out while paired with the sliders I have installed. 6 keycaps fell right out because they don't even have any resistance at all on the slider. I tried these six against every single other slider I have (I have 2 sets. One red/orange? and one blue). All of the sliders fit loosely on those 6 JTK keycaps. There are many other keycaps that have varying degrees of fit. Some fall of by just touching them, some I have to gently nudge off, some I can pull off easily with two fingers, and some are a good enough fit.
I then tried all my sliders with three different Cherry sets, and I found that the sliders would fit well on the keycaps that had no issues, but if a slider was loose combined with one keycap all sliders would be just about as loose with a super tiny difference between a few sliders.
I used about fifty sliders (pretty bored of trying sliders and keycap combinations at this point) to test with 50 different DCS keycaps made by Signature Plastics, and I didn't find a single slider to fit loosely at all. Great fit without any problems. I don't have any DSA or SA from SP at the moment or at least I couldn't find any, so I was not able to test those profiles.
I only have one PBT OEM set, but all the 50 sliders I tested were a great fit in the whole set. Maybe a tiny bit easier to remove on some keycaps, but still very nice fit.
So after spending way too much time on this I found that Cherry and JTK fit loosely a lot of the time. If the cap was loose on a slider from JTK then it was almost always as loose on a Cherry keycap. However the Cherry keycaps were generally less loose of a fit.
Again; if a keycap was loose on one slider, it was almost always (99%) as loose on another slider. And if it wasn't the same amount of loose then it was barely noticeable that there was a difference.
I unfortunately don't have the keycaps, will, time or want to spend more time trying to figure this out in more detail. I might post my findings if I ever end up getting my SA penumbra set so I can pair it with my FC660c, but don't hold your breath on that one.
I honestly hate posting stuff like this.
