Restructuring a RAID

I have 3 matching 2TB HDDs in my PC. When I first got the drives, I used them to help clean up a few older 1 and 2 TB HDDs I had, then once everything on the older disks was sorted, I wiped them and created a single dynamic disk (5588.67GB) out of the three.

I've noticed that the more I put on this dynamic drive, the slower and slower it becomes. I now have just over a terabyte on it (1053GB), and it can take over a minute (though usually closer to ~45 seconds) just to open the disk in windows explorer. Once it is opened, it performs slightly sluggish compared to a typical HDD, but not as bad as that initial opening. Similarly, if a file open or file save dialog comes up and I want to use the dynamic drive, it takes a minute or more to access the drive.

I am now thinking it would be best to either break these into individual drives, or look into some other actual RAID array for them instead of just a dynamic volume. I would really prefer a bit of security against disk failure, so that is another reason to go with some type of RAID.

My problem is that I only have about 200GB free spread across the rest of my HDDs, and if I try to back it up to bluray that is like 40 or 50 discs - not counting the time to back up to 40 or 50 discs, that is about $50 or so in discs; I could get another 1 or 2TB drive for not much more (not that I really want another drive at the moment).

So... since the amount of data on my dynamic volume is about half of one of the individual disks, I was wondering if there is any way possible to somehow maintain the data on one of the disks while removing the other two from the dynamic volume; I would think that would speed up the access time until I can slowly back the data up, or buy another HDD to move it to, or whatever else may come along.

If that isn't possible, what can I do to improve the access time of this drive? I have made sure it is defragmented, I keep it indexed for searching, and have tried turning on and off file compression with no noticable difference in the access times.

I am running Win7 64bit, on a i52500k CPU in a Gigabyte z68XPUD3 mobo...if that makes a difference. The three drives are each Seagate Barracuda Green 2TB SATA (64MB cache, 5900 RPM).