Orchestranova,
Yes this RocketRaid eSata card is fine for your early 2008 Mac Pro (giving you an affordable / Raidable Sata III upgrade)...
If you're only planning to use a single SSD, the speed will amaze you.
RunnIng two SSD's in Raid 0 is unbelievably fast. You have to see it to believe it.
All this made possible by RockefRaid's true Sata III 6gb performance.
As for the SSD itself. You can't go wrong with the OWC EXTREME Pro 6g.
P/S: If you don't intend to run in Raid, and you don't need to BOOT, a 6g Sata III card can be had for less than 50 dollars on the very same OWC site.