All good advice / notes from HungerMechanic. I think there probably is a trade-off between pre-load punchiness and silence. That said, I think a long spring on the lighter side can still be quiet enough with oil.
With the U4-in-Lime combo, I feel like the Lime’s stock spring is plenty in-context. The bottom-out weight isn’t as heavy, but the tactile peak is enough to prevent me from making accidental presses with my clumsy fingers. There’s a tiny bit of ring to the stock Lime spring with the U4 stem, but I have to have the switch right next to my ear to hear it - it’s more quiet than a stock U4 switch.
As for the stages thing, if it makes a difference on its own, I’m not really sure what it is. I think the amount of pre-load matters a lot, and I’ve seen it said that more stages allow for more of that, other things being equal. IDK.
Longer definitely means more pre-load (other things being equal) - and that means a snappier feel compared to shorter / less pre-loaded springs of the same bottom-out weight. The Lime has a pretty long spring, so even though it bottoms-out more easily than a Boba U4, I think it also feels more lively with the same stem.
Re: filming and wobble - I’ve actually had wholly positive experiences with filming silent switches; better stability, better silence. All the films I’ve used are clear of the stem’s path if installed correctly, and will prevent top-out tick that can mar an otherwise hushed experience.
Anecdote: I built a keyboard for a friend, and had the whole thing together only to find it dissatisfying, realizing that some switches top housings were jostling on top-out - so I broke the whole thing down and filmed all the switches. Oof… but after I was done, not a chitter-chatter to be heard, and the switches felt more solid. Three years later my bud still tells me how much he likes using it - also incidentally a U4-based franken situation.
Limes (and Peaches) do have wobbly housings - though I got some V2 samples today and the ones I have seem a little better about that, plus they have 5 pins. If I were doing a build based around Lime or Peach housings of either version, I’d probably plan on filming them.