HP PL DL180 G6, backplane, P420, SATA3

Hi,
We have a DL180 G6 with three 850 1 TB EVO disks and p212 controller (we are using the Adapter Tray from 3.5 to 2.5)
The current speed is kind of slow, and ACU shows that the drives are connected via 3Gb/s link

As the P420 is SSD optimized and a much faster card it should improve the speeds
The question is those the card support the SATA 6Gb/s speed and those the backplane affect it (as I understand it's just a pass-through)
http://www8.hp.com/h20195/v2/GetDocument.aspx?docname=c04111534