Problem understanding why internet bandwidth speeds vary with usb wireless gear

Would appreciate input into understanding why a NetGear 54Mbps USB 2.0
adapter produces a bandwidth speed of900+ Kbps and then when using a
different NetGear 54Mbps USB 2.0 adapter it will only produce a speed
of 140+Kbps.
My system setup is as follows:
I am transmitting a signal from my office, using a flat panel antenna
(Model FP19W 19 dbi gain 2150m-2700 mhz), to my house (.7 miles away)
At my house I have a similar flat panle antenna that flows to a bridge
that flows to a Linksys Workgroup Switch EZXS55W
Version 3 that flows to DLink Access Point DWL 2100AP.
In my Dell Inspiron 9200 laptop I have an internal Intel ProWirless LAN
2100 3A Mini PCI Adapter. When I use the internal wireless I seem to
consistantly generate bandwidth speeds of 140 to 150 Kbps. However,
when I disable the interenal wireless and plug in my son's Netgear 54
Mbps USB 2.0 wireless adapter it generates bandwidth speeds of
900+Kbps. Thinking that it was a problem with my internal wireless I
went out and bought the same Netgear wireless device my son was using.
When I fired it up it would generate speeds of 140Kbps. When the DHCP
assigns an address of .201 to the Netgear wireless device that
particular piece will generate speeds of 900+. Because the DHCP will
lease out the address for a specific time period. When I plug in the
second Getgear device, and the DHCP assigns an address of .202 that
device will only generate speeds of 140+.
When I take my laptop back to my office the internal Intel
wireless device screams at close to a T2 speed.
I even went out and bought a DLink usb wireless device. It generates a
similar 140+Kbps.
Any thoughts or recommendations on how to achieve consistant bandwidth
speeds of 900+ Kbps.