If you have multiple hard drives, use them.

Put your main copy of wow on a drive by its self, then put the slaves on a different drive.
Move the data/cache folders out of the slave wow folder (move not delete incase you need to move them back to patch).

ex:
c:\Program Files (x86)\wow2\Data -> c:\Program Files (x86)\wow1\Data
c:\Program Files (x86)\wow2\Cache -> c:\Program Files (x86)\wow1\Cache

You do this with the 'mklink' tool.

1) Remove the Data and Cache directories in each clone wow folder (or rename them)
2) Open up the Command Prompt
3) Change directory to the clone wow
> cd c:\Program Files (x86)\wow2
4) Make the link
> mklink /D Data c:\Program Files (x86)\wow1\Data
> mklink /D Cache c:\Program Files (x86)\wow1\Cache
5) Repeat for each other clone directory

Doing this reduced my lag in shatrath from horrible to zero.