In practice USB3 takes a bit of a hit, not quite saturating SATA-II speeds in write but exceeding them in read, 260MB/s and 340MB/s respectively with my 240GB Envoy Pro EX SSD. And it is stable, I think at the end of the day, I can handle the speeds in exchange for that and the fact it is only taking up one PCIe slot.
I also think it is a bit unfair to expect this card in my MacPro to equal the performance of the Envoy via the new 13" Retina's USB3 port feeding a 1,000 MB's 1TB PCIe SSD, that damn thing blasted a 202GB folder of RAW files across at an average of 520MB/s, peaking at 550MB/s...that's just nuts for a bus powered USB3 device!
So for now I am staying put. I definitely value all the input, hopefully someone will value mine on this comprehensive thread.
Hi Macshroomer. I am using the FASTA 6G USB3.0-eSATA combo and so far works fine . I know the card is not the best brand and does not yield maximum speed but I am happy and satisfied. As long as it's faster than Firewire 800 that's acceptable. Though I have tried the FASTA USB3-eSata together with another PCIe card so I could not comment on that.