"What part of the Amiga is limiting the speed? The ethernet card? The 68060 or the PPC? All these parts? ( I suppose the browser is run by the 060.)"
I'd say that with 060 it's depending of the bus and ethernet card, but with 040 and lower the cpu comes to limiting factor. I have had 10Mbps line for long time and I have used Hydra's Amiganet1.1 in zorro2 and realtek-based pci-card in Mediator. Both on the same a1200/060@66. Maximum speeds I got with Hydra were around 600kB/s, but with pci-nic in Mediator I can get the full use of 10Mbps line. Maximum speeds are now over 1MB/s in good "weather"
Normal speeds are 700-900k/s.
