Need input on a system

Hello all, I've got this system for some time now and it's working fine. Some input on future upgrafes would be usefull though. Here it is.

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MOBO: ASUS P5K PRO
CPU: INTEL CORE 2 DUO E8200
COOLER: COOLERMASTER RR-CCH-L9U1 HYPER TX2
GPU: ASUS EN9600GT/HTDI CUDA 512MB
RAM: KINGSTON KHX8500D2K2/2G HYPERX (2X1GB) + NVIDIA SLI-READY (2X1GB)
PSU: OCZ NVIDIA SLI-READY GAME XSTREAM 600W
HDD O.S: WD5000AAKS
HDD STORAGE: WD5000AAKS x 2, WD1001FALS CAVIAR BLACK, WD2500AAJB, WD1200AAJB, WDH1U5000E MYBOOK
All the hd's are on 2 x THERMALTAKE A2309 I-CAGES
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So questions now:
1) I've found a ASUS P5N-T DELUXE at half of it's original price, so I'm thinking of buying it and making an SLI later on.
2) I'm also thinking of getting a raid 5+0 up with the 3 500GB WD's but I'm not sure if that raid supports both good speed and data back up, if someone cared to explain about that raid.
3) Finally I'm not sure if my psu power can put up with the addition of a highend mobo (the ptn-t deluxe I mentioned), a 2nd 9600GT & possibly another 1 TB drive.

That's all I can think for now, any input will be appreciated. Thnx in advance.

1) There is nothing wrong with your current motherboard and I consider it far superior to any nVidia based motherboard. You will see much better performance gains by purchasing a new 4850 or 4870 over buying that motherboard and SLIng your 9600GT (should cost less to).

2) Skip the RAID. It is a PITA and the small boos in speed is not worth losing all your data when something goes wrong.

3) Your PSU is fine.

4) Try manually setting your RAM speed, timings and voltage in the BIOS. The P5K Pro supports DDR2 1066 speeds naively, it just needs to be told to use it. As long as you keep the RAM voltage to it's specified voltage (see it's manufacturer product page for it's specified voltage and timings) you will not void any warranties.