I'm having a similar problem...Slow web page loading, however, I get fine speed tests.
The issue is just a terribly long delay on OS X before the page begins to apprear in the browser, and then when it finally begins, it seems to come in bursts, and takes forever to finish the whole page.
I have the Motorola SB4100 running on Charter cable. My XP machine works fine. All upload/download tests are fine on both XP and OS X. It's just the slow web page loading (long delay before start). I even downloaded the latest FireFox, to test it, but no help.
I'm running OS X 10.4.8 (the ltest update did not fix my problem, as reported by others with the slow upload/download spped problem).
This is a strecth, but it worked: I loaded WinGate Server on the XP machine, and assigned the HTTP proxy on the Mac to point to the XP/Wingate Server, and boom! web surfing is now fine. But, I do not want to keep my home network set up that way.
A Linksys router sits between the machines and the cable modem. The performance is the same on OS X even if I remove the router and go direct to the modem.
It sure seems like that stupid Motorola modem. Some say 10.4.8 fixed the problem of upload/download overall speed, but I don't know about this slow web browser surfing problem. It hasn't fixed it for me. The XP box is always fast, but the Intel iMac is usually slow.
Some people named this DOCSIS thing in the Motorola SB 4100 as the culprit and say that a D-Link DCM-202 modem will fix the problem, but it seems to be DOCSIS also, so I do not know if I should buy one just to find out. Plus, how can I know is that modem will work on Charter cable. Is there a chance it will not?
Any advice will be greatly appreciated.