"Back in the days many SSD vendors were only focusing on high peak performance, which unfortunately came at the cost of sustained performance. In other words, the drives would push high IOPS in certain synthetic scenarios to provide nice marketing numbers, but as soon as you pushed the drive for more than a few minutes you could easily run into hiccups caused by poor performance consistency. Once we started exploring IO consistency, nearly all SSD manufacturers made a move to improve consistency."

http://www.anandtech.com/show/9144/crucial-bx100-120gb-250gb...