i did one test today for USB speed comparisons. not a very proper and reliable one though:

i reflashed PR1.2 to see what USB speeds can be achieved while using flasher3.5... i booted the n900 in flasher mode (holding u+connecting the usb cable) ...excellent mode for testing i think - since its basically the cleanest environment to test max hardware speeds.

i averaged at the speed 13602 KB/s while continously writing the 170mb flash file... the smaller flashes bursted at higher rates though .all according to flasher3.5's verbose text output.

in comparison to that i never reach speeds above 6000KB/s when connecting the N900 in mass storage mode (while maemo is running in the background). it should be caused by one of these reasons:
1. maemo os hogging the system so much that the overall system speed suffers
2. while running maemo, BUS bandwidth is overloaded with IO tasks to other hardware components.
3. less optimized drivers in maemo.
4. unknown reason?

ps. actually im not sure if it was the N900's, or the laptops usb speed that got maxed out during the test. i should have tested with a max spec USB2 port on another computer.