Windows 7 very slow with RAID 1

Your HDDs are running @5400RPM, not @7200 used by the Black and Enterprise HDDs. Please read WD's recommendations for RAID, they highly recommend the RE HDDs, not Green and not Black.

I strongly recommend you ignore RAID completely and simply use a backup utility like Acronis True Image to backup your Windows drive to a second hard drive.

The new version of Acronis TI has several options. It's a small learning curve, but you can Automate the entire backup procedure such as once per week or month, creating only 4 backups then deleting the oldest one.

On top of this, I also recommend putting Windows 7 on a 120GB SSD such as the OCZ Vertex 3 which is incredibly fast compared to a hard drive.

If you buy an SSD, install games to the hard drive. My STEAM folder is on my hard drive not my SSD.

You can CLONE Windows to an SSD or separate hard drive to avoid reinstalling. If you reuse an existing hard drive you'll need to find a non-RAID drive to temporarily make an Image to (or CLONE) then restore the image (or re-clone).

Summary:
1. Ignore RAID.
2. Buy Acronis True Image and setup an automated backup (learning curve).
3. Buy an SSD.
4. Clone to avoid reinstalling Windows.