If you don't want to mess with Raid, which is ok, then I would get the for you OS. Then make a smaller 10GB partition on 300GB drive for pagefile. Although you have plenty of memory, you'll be cutting down seek\access times this way.
Also one comment about the Ram, 4GB is pretty intense, you could bump up your video card if you take away a GB or two, or the Raptor.
Looks like a nice rig though, Cheers!
If your are serious about getting a Raptor for your OS and a few other Apps. I would get a smaller 36GB or 76Gb drive to save a little cash, unless you want the space. Just make a 10-15Gb partition on one of the other drives for your pagefile. Sounds like a nice rig.
I would check on the memory cap for 32 bit as well. I just built my first comp and I think I remember seeing something about 32bit not recognizing over 2 gigs RAM. I'll check my MB manual when I get home tonight and see if it said anything about it in there.
I think it's best if the windows pagefile, photoshop scratch disk and image files are all on separate drives. The way I've got my own PC set up is:
disk 1 - OS & apps
A partition per OS & swap partition per OS. A separate swap partition helps with defragmentation. About 10gb per OS does me but YMMV.
disk 2 - data
Partition this any way you like to help organise a large drive.
disk 3 - scratch disk & backups
Partition for Photoshop scratch disk, CD burning, audio recording or whatever else you need a scratch disk for. The rest of the space for data backups & OS disk images. One day one of these drives will fail...