In File System Properties, you can increase the read-ahead buffering on HDDs and toggle Write Caching on removable drives.
I just measured 877000 Bps with System Monitor on a 30MB copy from PNY USB3 32GB in 4-port mini-hub to IBM 6GB PATA HDD over USB1.1(UHCD) on Win98fe. There is also a PNY USB2 64GB, another 16GB, and a mouse in the hub. I have a USB2 PCMCIA card, but don't use it--I'm happy enough with what I have. The hub acts as a docking port and backups (with write caching enabled) and searches are fast enough.
Another copy from the PNY USB2 64GB had the same peak speed, but fluctuated slower. HDD has DMA enabled and all are Int 13 units: "If this feature is enabled for removable drives, the media must be in the drive when you start your computer." (But the 16GB works just fine when hot-plugged.)
All three thumb drives use Lexar JumpDrive2 drivers, but the 16GB is labeled: "Non-Lexar USB ThumbDrive". I think this one is rloew's mod.
Defragging the HDD can also help. Also test searching for text on the USB drive; this will read without any writes to the HDD (a bit faster than copying here).