The problem appears to be transmission over the SATA bus. Basically the data leaving the drive is being received with lots of errors, so your computer is having to re-request the data many times and this is causing your slow downs. This could be caused by various things:
1) Bad SATA cable or bad connection. Try a different SATA cable and SATA port.
2) Cable is running past a component or other wires that are causing interference, so try making sure the SATA cable is routed away from other cables.
3) A fault in the SATA drive or the motherboard.
You can sort out 1 and 2, but if that doesn't help looks like something is faulty.
I tryed running the same cables on my old disk that was running windows xp, and everything is okay there.
But the SSD disk is running at normal speed now, tough i get warnings from windows 7 that its a bout to fail any time soon every now and than poping up on the screen.
If things are running better now it might have been the cable. If it is fixed then the End to End error count will not be incrementing anymore. Eventually the drive will hopefully decide the problems are gone and it will start reported "Good" again and you will stop getting the warnings.