Guess that'd be me. I do believe the Izumi V is the best chain ever made, with the old Regina CX excepted, perhaps. I think that if silence is important to you, the chain is the most important place to start and the Izumi V is the only game in town. In my experience, I have never seen a KMC 1/8" chain run quietly. Folks on this site have disagreed with me, and while I have to admit that what I haven't seen is a lot, I have my doubts about quiet KMCs. I think perhaps definitions of "quiet" vary.

Cogs are a part of it too, of course, and unfortunately my experience is getting to be a bit out of date. There are some cogs out there that I haven't used. Campagnolo, Shimano, and Suntour all make/made good cogs. IMO most of the rest are least one step down, and some several. I never liked EAI, despite some good reviews around here. Perhaps they've improved, but they used to come with sharp edges that made noise, and threads that were slightly different from the thread on hubs from the "big three". The new EAI Superstar cog is perfect, though.

Most chainrings work quite well, in my experience, including those from Sugino. I takes a pretty bad ring -- or a bent ring -- to add much noise.

If your bottom bracket or hub is adding to drivetrain noise, it's seriously f*cked and you've got bigger problems than a little noise. If your bottom bracket or hub is adding to CHAIN noise, you need to lower your dosage, mate.

Mismatched components can contribute to noise, as the chainline needs to be absolutely perfect, and I mean to less than a millimeter. If a straightedge held to the ring and sprocket show even a slight deviation, you're going to get noise. This deviation can be introduced by something as small as a Campy hub with a Shimano crankset. The folks riding conversions made up from stuff laying around the garage are likely to encounter some really amazing chainlines, and they'll make noise, at least until the chain falls off. Spacers can be your friend, here.

Lube is important. Wet lubes are a prerequisite for a quiet chain, in my experience. Do what you will with your mountain bike, but wax, White Lightning, and other "dry" lubes will result in a noisy chain on the FG. If not immediately, then soon.

And tension plays a part too, of course, but not as much as some folks think, at least as long as a great chain is used. With the Izumi V, you will be fine if the chain isn't bar tight or dragging on the stay. That's a slight exaggeration, but then, it's only a slight exaggeration! Lesser chains are more sensitive about tension, in my experience.

I think that about covers the subject. All this, BTW, applies to 1/8" chains. A very simple way to achieve a quieter drivetrain is with 3/32". The 3/32" is more likely to unship, in my experience -- the results of bad chainline and/or poor tension are more severe -- but all other things being equal, road chains are usually quieter.

HTH!