QUOTE(scyap @ Dec 18 2011, 04:35 PM)
But thats only like 10% speed...
Its like subscribing to Unifi 5Mbps and getting 10% speed only (64 KBps)
or buying a Ferrari which claims it can do 300 KM/h but can only hit a top speed of 30 KM/h !!!

It isn't 10% of the speed.
SATA 3.0 Gbps uses 8b/10b encoding, leaving only 80% for the actual data transfer.
So,
80% x 3 Gbps = 2.4 Gbps
2.4 Gbps = 300 MBps
Or at least that is the theoretical number. Real world tests on SATA 3.0 Gbps with SATA 6.0 Gbps SSDs has revealed that the practical maximum speed is about 265 MBps.

And your HDD test is flawed because it is like driving your Ferrari from A to B to A in
t time and then claim it takes
t time to drive from A to B, which is what you actually did in your HDD test. The more appropriate test would be for your CPU to write to the HDD,
which has seen numbers up to 150MB/s in typical HDD benchmark tests.
The moral of the story here, is unless you know what you are doing (like being intentionally misleading), use proper benchmarking software to benchmark.
tl;dr: It is 56.6% (practical) or 50% (theoretical) and not 10%.