Can I simulate a slow hard drive?

Use nbd, the Network Block Device, and then rate limit access to it using say trickle.

sudo apt-get install nbd-client nbd-server trickle

# echo 1 > /proc/sys/vm/drop_caches

That'll slow you down :)

It'll force you to read from disk, instead of taking advantage of the cached page.

If you really wanted to get sophisticated you could do something like fake a read error every nth time using the scsi fault injection framework.

http://scsifaultinjtst.sourceforge.net/

Have a USB 1.1 hub? Or a slow SD card? They'll get you down to under 10mbps.