flow comparison USB vs PCMCIA

I was wondering if anyone could explain the following observation?
I am comparing the data flow to the very same laptop having two
interfaces alternately configured.

asix chipset 10/100 USB 700KB/s (+-15)
3com 3C574 16bit 10/100 PCMCIA 880KB/s (smaller fluctuation)

So not really as bad as I thought but a very discernable difference.
It would appear you pay a high price for USB unless the implimentation
is poor?
This is a gentoo system 2.6.18 kernel.
The rate info was derived by copying the same dvd image from the same
server in the same room as laptop.
Each interface was using the same port in the switch. (ie I moved the
wire)
Could this be attributed to the magic or manipulation in the usb
bridging?
The asix chipset is in a targus USB dock.
http://www.targus.com/us/product_det...sp?sku=ACP45US
Or could this be the low horsepower of the laptop a 380XD thinkpad at
233mhz? Perhaps the usb is dependant more on horsepower than pcmcia due
to the externalization of the bus.

Thanks for any info.
-Walt

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