First and foremost it is still way faster than a HDD!!
.. Yes 500 mb/s seq speed sounds impressive compared to your 203 - BUT Seq Performance is the LEAST important performance matrix for a OS = Program drive. Over 50% of your files will be under 32 K and a good % under 8 K and they are Randomly spaced. Reason RANDOM reads are the most important matrix for Booting into OS. And your Random reads are still 14 X faster than a HDD.
Not sure, But I think you are limited by SATA II interface.
Also while the Nvidea driver works it is NOT optimized for SSDs.
To get the "ADVERTIZED" performance the SSD would need to be (A) on sata III (6) and (B) on an Intel chipset, running the latest intel RST driver. (NOTE AMD driver is close)
Worst driver is the "marvel" driver for the older SATA III (6) Pci-e card (I have one) and the NVidea driver.