yes it has been mentioned here before few times,
the reason for that band sparing is to give the operating system a passway to the net .
that passway which is made out of that spared bandwidth will be used
for the most to alow windows security update at all times
as i understood the idea behind that xp option is
that you can normaly use all of your bandwidth (100%),
as a system default anyhow ,
and the system will limit it only when it needs to
for example, if it needs to update
which is good thing by itself and hapend only once in a wile ,
at the rest of the time, and if the system is operating properly
than it wont bother your bandwidth .
tweaking that option is a bit like building a "sophisticated gate"
across the road (the road stands for your bandwidth),
and than forcing that gate to stay open at all times ,
i have to add that i'm a bit weary from speed tricks ,
changing and booting , booting and tweaking .
you can't made gold out of lead .
i didn't notice any speed change , and the only noticeable cupping
is the one enforced by the internet provider , and to change it you'll
need to pay .
but this is only my two cent comment .