So far I've only found two of the Stealth magazines and have no points in the Sneak perk. If I wear power armour they find me pretty quickly, which is what I'd expect. If I use Shadow Combat Armour they go cautious and if I stay still they eventually go away most of the time, unless I'm in a narrow passageway and the only way they can go is towards me.

I find the Suppressor weapons work perfectly fine, on pistols anyhow. I have yet to get a Suppressor Sniper rifle yet. Bear in mind your perk level in Stealth, how many Stealth books you have found, and your gear you are using all play apart as to, whether you get detected and how quickly. Not to mention, the lighting available, the speed you are currently moving, the weapon you just fired. Every detail matters.

I don't use silencers. I want my range. I don't mind if enemies hear my shots, as I can use the environment to take cover easily.

Range mostly affects VATS capability. I don't think it has a particularly noticeable effect on damage.

The silencer makes it so that the NPC's don't know where the shot is coming from. But if they see another NPC dying then that still puts them on alert. Which makes sense to me.

I don't know if it's my game, but I think stealth can actually be broken.

I was at Slocum's Joe Corporate HQ at a low level wearing T-45 PA, walking around, and bright headlight on clearing out the building. Eventually I get to the top (?) floor with three raiders trying to break into a safe. Even though I was in this heavy armor with my spotlight on, they didn't notice me until I was just about to pass through the door frame 3-4 feet from a standing raider.

Something similar happens elsewhere as well.