ClassObject is correct. On the older mac pros 2006-2008 you have two extra ports on the 2009+ you have 1 extra port. So the extender cable will work. But yes it is eSATA 2.
Thanks all for your replies. As for now I have two pcie lanes open. At $12 I might as well buy two of those cards. Will this prevent my ssds from being throttled???
That was confirmed by nano in the other thread you linked to. Fortunately for me I have lanes 2,3 and 4 available at the moment and will use lanes 2, 4 with the apricorn velocity solo x2 I just got from amazon. Thanks for your help.