fastest raw device copy?

[Christoph Kukulies]

Hi list,

I'm considering using a bootable USB stick with FreeBSD to perform a 
backup of my notebooks'
500 GB hard disk to a physically identical (same make, same type, same 
size) hard disk attached to  USB.

What would be the fastest way to do that sector by sector copy? I'm 
using dd right now,

dd if=/dev/ad0 of=/dev/da0 bs=10000000

but maybe there is a utility which does this faster or a larger buffer 
size? Probably the limit will be
the USB 2.0 bus speed anyway?

--
Christoph