extreamly slow read/write from/to USB stick on 5.1_RC3

Several day ago I wrote about slow read operation from my USB stick
on 5.1_RC3/amd64

http://mail-index.netbsd.org/port-amd64/2010/07/12/msg001210.html

Today I tried to write to the same USB stick rather big image, about 700
Mb in side and found that write speed is drammatically slower, about
170Kb/s.  Any clue?

Command is: 

dd if=huge_image.img of=/dev/rsd0d

-- 
Best regards, Aleksey Cheusov.