How can I improve the annoyingly slow internal speed on my home network?

How can I improve the annoyingly slow internal speed on my home network?

My network is already set up and has been working for "a while". I have
wifi and wired internet on a bunch of devices and stations (more than I
care to admit), the gigabit router is working and configured. Everything
is wifi g or 100mbit or newer. I recently reloaded windows on 3 of the
most used stations.
My cap to the internet is 16mbit/1mbit which I just ran off of
speedtest.net (and realize that i need to bang on TW for not giving me
anything close to 50 like I'm supposed to have). Everything can be running
like netflix, steam games, bittorrent, etc etc, concurrently and there's
no problems.
But when I go to copy files from one station to another, I can never seem
to crack 20mbit. It doesn't cap at 20mbit (I watch using the excellent
networx http://www.softperfect.com/products/networx/), it vacillates up
and down and never quite seems to manage ~20mbit. On some stations it
never even gets close to that even tho I have no 10mbit nics in the house.
Right now I'm copying my library of music production source files from a
pc to laptop. The files vary in size from a couple megs to a couple gigs.
And I realize that copying 1k * 2mbyte files will be significantly slower
than 1 * 2gbyte file, but even on the big files, it doesn't pick up. But
between to gigabit nics, wired, I would expect it to be >20x the current
speed.
I would expect that, even between 2 wireless g devices, I could get >
40mbit with the tech cap being 54mbit, and that between 2 gigabit
stations, that i could get > 500mbit (reviews say they got 700
consistently)
Note: I'm not trying to get 100% advertised speed. I know that's not
really attainable in windows. I would just like to use the tech that I
have on my machines.
This has been a consistent problem for as long as I can remember, spanning
routers, windows reloads and various devices with the only constant being
my home office work pc... and even it's only constant for a couple years.
This is actually the reason I bought this router like a year ago. However
today it finally got on my nerves when the file copy is telling me 4 days.