What to do with 3 WD6400AAKS ??

I was thinking of upgrading the storage on my PC, since I need more space, and specially cos I want better transfer rates.
I feel like having just one single drive is sometimes being a bit of a bottleneck for my setup, since I keep everything there (OS, documents, games...), and just use my 2 extra PATA drives for downloading and for backups (300GB each). The disc Im using right now is a WD6400AAKS


So, I checked prices and my conclusion was that now, where I live, Spain, WD6400AAKS are probably the best affordable hard drives, and have also one of the best size/price ratio I can buy at 55€ each. So.. the one I have works great, why look somewhere else when everything is pointing in that direction ??

Now the dilemma:

1 have around 100€ to spend... I could buy 2 WD6400AAKS with it; Does it make sense ?? Would it also make sense to use the 3 of them for a RAID 0 array ?? Or just with 2 of them and keep the 3rd for additional backup ?? Is there a noticeable performance increase from using 2 to 3 drives ??
I was also thinking of using Intel Matrix.. then I could use a smaller 0 raid for OS/games, and then RAID 5 for documents; Im just a bit unsure about the RAID 5 write overhead, its overall performance compared to RAID 0, and specially about how easy would really be to recover data if there are problems. I´ve read quite much about RAID, but not much about how to proceed when something goes wrong, so Im unsure about trusting all my important data to a RAID 5 system, which is part of an Intel Matrix array... sounds a bit tricky, but maybe it just sounds and it isnt ?


Please dont hesitate to forward me to other posts... I´ve really been reading quite much, but there is so much info around that it´d be easy to miss part of the interesting stuff.



Oh, and here is my setup in case it helps (or so you can advise me to save the money of the 3rd drive and put it smwhere else



Intel Core 2 Quad Q6600 G0 2.4Ghz FSB 1066 8MB Box
Asus P5Q-E Socket 775
Arctic Cooling Freezer 7 PRO Socket 775
A-Data Vitesta Extreme Edition PC2-6400 2x2GB 4-4-4-12
Western Digital WD6400AAKS 640 GB SATA300
Antec Nine Hundred
Corsair TX 750W
Sapphire HD 4870 512MB GDDR5 PCI-E



Thank you in advance !!

no one ?