You should break out the RAID's like thus:
256 GB - OS and Programs
600 GB - Projects
600 GB - Scratch/Cache
240 GB - AE Global Cache
1.5 TB - Media
1 TB - Exports
1 TB - Backup and Archive
Jim, I completely agree considering your own system, but not on Ulf's system, which is way faster than yours.
If you want to add another two disks, I suggest:
C: 256 GB OS & programs & pagefile, SATA 6G
D: 240 GB Windows temp & media cache & AE cache, SATA 6 G
E: 2 x 600 WD in raid0 on the Marvell controller, previews. SATA 6G
F: 4 x 1 TB in raid5 on the LSI for media and projects
G: 1.5 TB exports and backup.
FYI, yesterday Bill gave me some experimental figures on the new test we are working on. Exporting a two hour timeline on an i7-2600K with a single OCZ Vertex4 SSD was around 6 times slower compared to a system with a heavy raid array. 84 seconds versus 14 seconds. Jim's suggestion to break out the raids you currently have will only slow down your system. In Jim's case he will not notice it, because his system is so much slower than yours, but you definitely will notice it.
The complicating factor in your case is the variety of disks you have and only a 4 port controller. The E: drive is way too big for previews only, but you don't have many choices for alternative uses and despite that they are older drives, in a raid0 they do give you nice performance. Going from 2 x 1 TB raid0 to 4 x 1 TB raid5 on that controller will give you added performance plus security against disk failure. Don't expect miracles in performance boost from 2x R0 to 4x R5, it will probably be only 25-35% or around that figure.
Thanks a lot guys - got something to work with now
@Harm: the 4 x 1TB you suggest in raid 5, is that with a hot spare or will I get 4 TB to use. And woul you make one volume only or two volumes on the raid 5?
Use only one volume on the RAID 5. Using two volumes on a single RAID 5 array will have the same effect as partitioning single disks into multiple volumes: Increased overhead, slower performance if anything besides the primary partition is accessed and increased and uneven physical wear and tear in the disks.
In addition to what Randall said, the 4 disks in raid5 are without a hot spare, for the simple reason you have only 4 ports on your controller. You will effectively have 3 TB of capacity, 1 TB is lost to parity, but that is the security you get. And I agree with Randall that you should not make more volumes on that array. Leave it as a single large volume.