There's a 'Tech TV' article on the QoS setting, that's at least two years old. Because there are a variety of reports on if it is good or bad, needed or not, and what the ideal setting should be, what they did was try them all.
In a nutshell, it just doesn't matter. Pretty much any setting gave the same results. Not exactly sure how it works, but I'm under the impression only software designed to use it will enable the QoS and there is almost nothing out there that will activate it.
Set it to whatever you like, doesn't matter.
There's only a couple of registry tweaks you can do for this, depends on computer type, and the all important ISP (eg. adsl & cable have differing tweaks).
Lots of articles telling you what to do, many are wrong. I find the link below to be the best. Not only do you get unbiased info, but he says why to do it, as well as how.
http://cable-dsl.home.att.net/