Drive is decrypting really slooooooow...

I am having an odd issue with Reallymine and I am not really sure what it is that I am doing wrong here. I have reallymine installed into DEFT Linux (Ubuntu).

First, a bit of back story,...

My client brought in a 4 TB WD digital drive that was "no longer mounting". Looking at the drive's SMART data I noticed that the drive was in not in the best of health. The drive has 14 uncorrectable sectors and the drive's spinup time is 7 seconds. I cloned the entire drive to an identical WD drive that I had in stock. I scanned my target drive and could not see a file system. After calling the client I find out that the drive was from a MyBook enclosure. When the drive stopped mounting the client pulled the drive from the enclosure and threw out the enclosure....d'oh!

Using the healthy drive that I had cloned the failing drive to as the source I ran the following command in Linux:

reallymine decrypt /dev/sda /media/root/Data/clientname/data.img

Due to bad weather and power outages my image process was cut short. After 5 days of letting the program run it had created an 80 Gb image of the target drive. I scanned the image just to see what the data looked like and found that there was some good data but I was still 500 GB short of the amount the amount of data that the client has on this drive so I started the process again. This time I tried running it on a more powerful workstation with dual quad core Xeon processors in hopes that it would speed up the process but found that it was decrypting the drive only a little bit faster than the Core 2 Duo workstation I was using on my first attempt.

From the descriptions that I have read online it seems like this process should be running faster than it is. At the rate I am going this will take weeks.

Any ideas?