The read/write speed to your drive can be limited by the enclosure, by the USB (or FireWire) controller in your PC or it can be limited by how the drive, enclosure and controller interact with each other.
The Transfer Rate Test and Write Speed graph show that you cannot achieve 16x with this combination.
When you try to write faster than the drive can handle, the Buffer Under-run Prevention feature in the drive will stop and start recording frequently. Some drives handle this quite well while others produce much poorer quality burns (lots of PIF spikes) when this happens. I'm not familiar enough with your drive to know how it works in this respect.
If I were you, I would limit myself to 12x burning with this setup.