[quotemsg=20409992,0,1559654]... it seems that fastests SSD's in 2.5" factor form reach ~550MB/s which still has plenty of headroom in SATA3 theoretical 750MB/s[/quotemsg]
Ten seconds in a search engine would find the answer. To quote MariusMatutiae from howtogeek.com:
"While data is actually sent at 6 Gb/s, it is encoded to counteract two common defects in telecommunications, DC Bias and Clock Recovery. This is often accomplished using a specific coding algorithm called 8b/10b Encoding. It is not the only encoding algorithm which has been devised to this end (there is also a Manchester encoding), but it has become the de facto standard for SATA data transfer.
In 8b/10b encoding, eight bits of signal are replaced by 10 bits of (signal + code). This means that, out of the 6 Gb the channel sends in a second, only 8/10 (4/5) are signal. 4/5’s of 6 Gb is 4.8 Gb, which in turn equals 600 MB. This is what degrades the 6 Gb/s channel into a mere(?) 600 MB/s channel.
The advantages obtained by compensating for DC bias and allowing for Clock Recovery more than compensate for this slight degradation."
In reality, with other overhead issues factored in aswell, SATA3 tops out at around 550MB/sec, as confirmed by PCIe models based on the same technology as their SATA3 counterparts.