(1) Down load and run AS SSD. Don't need to run the benchmark. Look at the upper left. It should show what driver is being used. Will also show/verify that partition alaingment os "OK". Should also show Firmware version.
(2) Verify that the SSD has the latest Firmware version (Check plextor support website) for latest Firmware. My Curcaial M4 is very simular and they recently came out with a new firmware that improved performance.
(3) Most benchmarks are performed using a Intel chipset, there may be a small performace diff between your chipset and the latest Intel ver 10.6 chipset driver.
Screen shot of My M4 using AS SSD
(4) As sminlal indicated, do not pay to much attention to Sequencial read/writes as this is the LEAST important paramenter for a OS+Program SSD. The small file random 4 k is by fare more important. Also Unless you use the same benchmark as the one you are referencing against, the comparision may not be valid. The most often quoted benchmark scores are use data that can be compressed - Real life the data does NOT compress much.