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.
Yes, I understand what you're saying. My point was that it's not SATA that's the bottleneck in these kinds of situations.