You might also check that you are using all USB 2.0 HIGH SPEED.  IOW, USB
2.0 specifies 3 speed settings and you might want to check what yours is set
for.  I saw a simialr problem a couple of years ago and found that my BIOS
had a setting for HIGH SPEED being on or not.  Once I changed the BIOS
setting, everything went faster.  I am not sure, but I think that was an
AMBIOS based system.