To get the kinda of redundancy your looking for you need to set the drives up in a RAID 1 (mirror).
This means that what ever gets written to one drives get written to the second drive, so if one fails you just pull it out and your good to go.
Most new motherboards will support a software raid and its fairly simple to set up, just refer to the manual.
The 5200 are technically slower, but should run cooler, which should add to drive longevity.
Hopes this helps