Update:
I took the two drives to Micro Direct this morning, after running Dban to clear the drives for testing.
They did a quick test on each drive (took around 10 minutes each) and they both came back fine.
He said to run a extended test at home, and write down any errors if something still isn't right.
The only conclusion I can come up with now, is that my Intel RAID controller isn't worth using again, and to just run drives as standalone.
Maybe it's the controller that has been causing all the issues on my drives.
Another thought, is because all the drives now contain only 0's, there won't be any bad sectors to test for using a quick test, so something could still be up.
EDIT:
Running extended tests on each. Approx 2 hours a drive