Your running RAID 5 on an ATA setup, and you are talking about not wanting to lose data?
I have seen a few horror stories of recent where people have lost the config on those ATA controlers when OC'n or doing anything out of spec on the system.
I think when it comes to RAID... OC'n and such that would mess with the PCI bus or power on the board should be avoided 100% or you will just beg to have that array turn into dust out of no where.
I know I dont trust my ATA arrays at all ( which is why all the data is also on tape
)