If you use a RAID array consisting of 2 striped disks and 1 parity (RAID 5) it can increase read speeds and times from HDDs. And, as said by Troy, hard disks are the slowest components in a PC. This allows for speedy reading b/c the data written is split between the 2 drives, and then a bit written to the parity drive. Having a parity also means that data can be reconstructed if one drive fails.
Edge the Raid Ideal as appealing it sounds I still see no reason for it.
If this seems too complicated, and just want to stick to separate HDDs, then do so.