Questions about "Q"

[Richard Iredale]

I am a new user to CCE 2.62, and I am trying to push MPEG2 as low a bitrate as possible. I note that there are two modes of variable bitrate, One-pass and Multi-pass. Once I create an mpv file I can look at it using Bitrate Viewer.

I have found that using the One-pass VBR mode in CCE produces a file that shows a very flat Q and a highly variable bitrate. Using the Multi-pass gives a more variable Q curve but the ability to fine-tune portions of the timeline.

My questions:

(1) Is "Q" an accurate method of measuring artifacts? In other words, will a lower Q always produce an image that is more artifact-free?

(2) If Q is the magic number to watch, and if the One-pass method produces a very flat Q line, then shouldn't this method be the one to always pick?

(3) Why does CCE's Q graph (found under the "Advanced" button) behave differently and show different values than the Q graph obtained with Bitrate Viewer? Which program is telling the truth?
(4) Just how low a bitrate can one use effectively? If I employ the anti-noise filter in CCE, then the graph shows a lower Q, but isn't that cheating? Aren't I losing sharpness by using the noise filter?

Thanks for any advice anyone might have...