I just posed a lengthy question on Micromat about Surface Scans in general, and also specific to TechTool Pro 8.0.3. I suspect I'll have the answer soon, and I'll post it here.

As part of that, there are of course a number of factors to consider regarding the speed of the scan (I also mentioned all of these in the post):

1. SSD versus traditional hard drives.

2. Internal bus speeds.

3. External connectivity (USB 2.0, USB 3.0, Firewire 400, Firewire 800, and Thunderbolt)

4. Amount of free space on a volume.