I can't say for sure regarding the whispers tactile since I haven't tried those, but comparing the U4 with the heartbeat the heartbeat is quieter, and feels just way, way, better. I would guesd that the whispers are probably on par with the U4, the tactile bump probably increases the sound just slightly over the linears. But the whispers I would assume have the U4 beat in feel.

Mushy is not the word, they have a slight cutout at the bottom of the stem which softens the impact a little bit but it's more like bending your knees a bit when landong after a jump compared to landing on a mattress. So not even remotely like the mushy feeling rubber dampeners have.

Zilents, U4, Cherry and Gateron silents. And then some UHMWPE linear switches which aren't marketed as silent but I do find them quieter than pom or nylon based switches and without any dampeners.

I'm not sure we're talking about the same switch

They are a normal linear switch with holes drilled in the bottom to allow sound to escape which is what makes them silent, so there is absolutely no mushiness.

Edit: haven't tried the whispers since tactiles aren't my favourite but I believe the whispers aren't quite as silent since that tactile bump produces a little bit more sound of course.

Haimu Heartbeat are the quietest switch I've ever tried and it does it all without rubber dampeners, so it feels exactly like a regular switch. Can really recommend for office use

I've always been curious about this. I get static shocks from doorhandles and my cardoors all the time, but have never ever gotten a shock from any of my keyboards. Maybe I've been lucky