I found out why my net4501 was going slow: the latest bios had the cpu cache disabled. :-) Its so nice when you finally get to the bottom of something.
To update the bios, I had to use linux. Even though Mac OS X runs BSD, I couldn't get the bios to update using minicom or lrzsz. :-(
I used linux, connected a null modem cable, and then booted up minicom and the net4501.
Old:
comBIOS ver. 1.31 20070408
New:
comBIOS ver. 1.31b 20070614
Is it faster? YES! It is WAY faster. It can load the system.php page in under 5 seconds, whereas previously it required 10-60+ seconds, depending on the configuration.
Would have been nice to get a notice from Soekris about this, but as imply on their website, customer service is not their forte. :-)
Thanks to the purple yonder for notes on flashing the net4801 bios using GNU/linux!