Well I did make it to the end, but speed read through it so sorry if i have missed something.
A few points
1) Having many disks hanging off your computer is not the best working practice.
2) Why did you use Softraid? You can make a RAID0 out of 3 drives in your Mac without extra software.
3) My advice, pull all disks out, put a fresh drive into the MacPro, do a new install of the OS, do all the updates then install FCP and do all of the updates. Add another disk, format it as unjournaled and make this your capture scratch disk. Does FCP run OK now?
If it does, add more hardware bit by bit until you hit a problem.
Peter