I have been following this one, but have been a little busy to comment. I am very convinced that the "USB 2.0" under Mac OS 9 is a Myth, since I personally tried over 3 dozen cards when this was important to me. Yes there were clearly cards with NEC chip sets that performed well under OS9 as far as stability with the devices they connected, but at 1.1 speeds; VIA always made crap, the cheapest PC Logic boards (VIA chipset), worst audio (VIA), etc. So it it wise to avoid them. I also made a note about... "DO NOT use any ALI based cards", but like usual I did not elaborate, so I am unsure what the issue was.
The whole point of USB was like all those horrendous WinModems of the past - the host systems had to provide most of the processing and management of the USB operations so that the USB controller itself is a cheap and relatively simple IC. Even at higher speeds than USB 1.1, connected devices could never perform as well as those connected via other means because the host system had to expend a lot of processing capacity to manage them.
Wow, that brought back memories and is 1000% spot on, We used to setup Fax servers and other modem intensive applications and "WinModems" were NOT usable. You needed to use a high quality US Robotics (non-win modem) or intel that had a dedicated controller chip. The results were awesome, handshaking without issues, and they never dropped the connections.
I also believe, that is why FW audio interfaces run flawlessly compared to USB even on Machines that support USB 2.0; the FW interfaces, when used with a good quality FW chipset appear to use less main CPU, but this is more of an overall observation, I never benchmarked the differences. Maybe, MacOSPlus can elaborate on this.
...or a server-grade fully-managed ethernet controller with its own processor and cache RAM for that matter, you'll know what I mean.
Yes, we would hang about 80 to 90 workstations on the same subnet with a Bus mastering Ethernet card in a Novell Server (Pentium II) and the packet stack never overflowed. Basically, all network file/print requests were being handled almost in real time with 1 Ethernet card !