nobley

I would second the comments about RAID 5. It has poor write performance compared to RAID 10. I would also suggest double checking your RAID controller supports SSD TRIM correctly. I've seen some (cheapo) controllers where TRIM didn't work in a RAID configuration and the SSD got slower and slower. Taking the drive out and running a manual TRIM on it fixed the problem (which then slowly got worse again in the original system).

In the past, I've seen a faulty drive slow the system to a crawl. This was usually accompanied by a "knocking" sound from the drive. Have you tried connecting the drive as a slave drive after the system has started? This sometimes works with SATA drives.