ESATA 6g, USB 3 on PCI, real world

Question

I am looking to buy a
CalDigit FASTA-6GU3
2 Port USB 3.0 & eSATA 6Gb/s Host Adapter
to put in my 2008 Mac Pro PCI slot to run an external Blu-Ray writer and hard drive enclosure off the eSATA ports.
Looking for info on what real-world Gps/Mbps the Mac Pro PCI slot can actually handle -- it is great if the card is 6Gbps eSATA & 5Gbps USB3.0 -- but the bottleneck is what the PCI bus can move (also limited by what the hadrdrive and writer can actually read/write).
I read on the reviews that the Mac Pro PCI bus can only perform tops 500Mbps (slightly above Firewire 400Mbps).
I also read the actual PCI card performance was limited to 250MBps due to its PLX chip design.
As USB2.0 is based on 480Mbps -- I have to wonder what all these numbers mean.
Can anyone put this into layman's perspective -- why put a 6Gps eSATA and USB 3.0 card in a PCI slot that is limited to 250Mbps?

Answer 1

Bytes will come to byte you if you think they are bits.
Kilobytes was the same issue. Or gigabits and bytes.
10 bits to a byte basically. sometimes 8 bits if there is no check bit.
Wikipedia is your friend, more so than Google. And there are dictionaries online of tech terms.
Some poeple come here talking about their MacPro except that they don't know what a 65lbs Mac is and my guess is there are a dozen notebook users asking.
The Sonnet E4P ~$250 w/ 4 x eSATA ports is nice for adding direct connect to SATA devices, more than enough bandwidth.
Your Mac has those four internal SATA2 drive bays. Those are all on a single shared controller bus, so while in theory you can get 275MB/sec max from each, there also is NOT full 1GB let alone 1.2 (1200MB/sec) but rather 750MB/sec - more than enough for most disk drives still. Only when you got to SSDs that it was more apparent.
Here is what your Mac's Serial ATA drives and bus are offering in bandwidth performance, sortof.
180MB/sec is about the max of 4TB enterprise drive, or WD 10K latest VelocityRaptors.
SATA2 SSD was about 275MB/sec also, and 450-500/550 (max, writes are often less with SSDs, reads tend to do very well, but it is the very high I/O's per second that they shine, along with lowest response time in seeks being 1/1000th - instead of being 4-12 milliseconds you are into less than 1.0 nanoseconds.
Geeks were happy with a Base2 numbering - binary 1's and 0's and base16 whereas Apple and others now wanted to change one gigabyte from being binary 1024MB and turn it into 1000MBs. The dumbing down of math, specs, and the i-ification  of consumer devices. iDevice, iOS and consumers that never liked those 1024 binary and hex based numbering system.