Sminlal, we might have had something similar pop up recently. We are waiting to hear back from the OP. He bought a PCIe 1x controller for his SSD and can't figure out why his read speeds are only ~200MBps. If he has this card plugged into a PCIe 1.0 port which tops out at 250MBps, then his 200MBps reading makes sense. He'd need to use a PCIe 2.0 which can move 500MBps if he wants his SSD to move faster. Not quite what you mentioned, but an example of how X connects to the system and you have a slow down.