SSD Not running all that fast

Hello, Im new to ifixit. I have just finished following the guide to install a Sandisk SSD 120gb Extreme into the spare space of a Mac Mini 2011.

I have cloned the 500gb drive that was in there and set the SSD as the boot up drive. I benchmarked the SSD using BlackMagic Disk Speed Test and got a max write speed of 130Mbps. The SSD according to Sandisk is rated at 510Mbps write speed. What i find peculiar is that my macbook air with the 256gb SSD tested having 250Mbps.

My question is if the drive is faulty or if it is something to do with the mac mini that is bottlenecking the speeds or if I can optimise it in anyway to achieve better speeds.

Thanks in advanced