The NewerTech is good if you would like to keep your sled.
http://eshop.macsales.com/item/NewerTech/ADPTADRV/
However, using the OWC Mount Pro (blue sled) is the best because the SSD goes directly into the Mac Pro drive controller. The NewerTech and Icydock both connect to a adapter which then connects to the Mac Pro controller. The additional adapter may slow bandwidth as you have an extra adapter in between. It's better to go straight.
Of course, if you can spend the $100, get the Apricorn Velocity Solo x2. On the sled, you get SATA2 3GB/s. On PCIe, you will get SATA3 6GB/s (given your SSD is SATA3).
Hmm, I see, I didn't think of that.
But apparently there's also a cheaper way of connecting it with PCIe, a member on the previous page explained:
For a single SSD, you can hit near peak SATA3 speeds with a cheap ($15) PCIe x1 card, connect via a longer SATA cable and put yer SSD in the optical bay.
http://www.ebay.com/itm/New-PCI-E-SATA-3-0-SATA-III-Card-6Gb-s-eSata-ASM1061-/150839174303
I'd be interested in this method depending on how it works. If it costs as much as a tray for the optical bay, obviously I'd go for this solution!
I like the idea of the SSD staying in the optical bay, but I'm confused as to how you connect it to that PCIe card. I've never hold an SSD in my hands before so I know nothing about them or how you connect them. I'll be buying the Samsung 850 Pro. Do you need to leave the door of the MP open and connect it from the outside, into these ports it shows on the pic?