What limits the rate of data transfer on a local area network ?

For months my ThinkPad T420 has been chugging along, running nMap-based scripts to gather
Internet address data. "Not quickly enough," I thought.

So I dragged out another ThinkPad T420, updated & upgraded it to the latest flidas spec's,
and started another batch of scripts to fill in the blanks.

Whereupon a revelation appeared: The System Monitors started displaying a limitation of
which I was utterly unaware:

When the data transfer rate on one 'puter goes up, the rate on the other 'puter goes down,
as though they're playing by the rules of a game that's not under the control of either
'puter. Also, the data transfer rate averaged between those two 'puters is about half what
it was with one 'puter running those scripts by itself.

The two 'puters are obviously on the same LAN, with each one connected wirelessly to the
router. They have no remote access arrangements of one to the other. The router is on its
own FIOS LAN, judging from the various locations where its server appears to b, from GPS
analysis based on its IP address.

I'd been adding scripts, each one running from its own terminal, until all the ups and downs
in the data transfer rate averaged out to a smooth, nearly flat wiggly line ... indicating
that more scripts could not extract any more data than the limiting rate, which was about
90 kB per second. With two 'puters, the total limiting rate is still about 90 kB per second,
so I'm no worse off than before.

Is there a way of nudging that limiting rate upwards ? I can access my router's admin page,
but there's no place I can find that suggests any control of the bit rate...

George Langford