You can't tell...that's the fun ( ) of overclocking.....it's always a roll of the dice.
OK, good decision. Didn't know if your audio software would take advantage of 4 cores.
Western Digital has their new 320/Gig per platter drives out, and the 640Gig model is only $130. THis means you only have two platters, and thus less noise, heat, and power. The higher the density of the platters, the faster the transfer rates are, and the faster the HD is (in general of course, access times and firmware play a big role as well). The Samsung F1 1Tb drive also has 340Gig/platter, so it only has 3 platters, but it costs $260, so you could get to WD drives for one Samsung, and end up with a bit more space. Samsung hasn't gotten their 640Gig version out yet, hopefully they will soon. The Hitachi and Seagate drives still use lower density platters, so they will have lower transfer rates and higher power /heat requirements.
Short stroking is where you partion only a part of the HD, and leave the reast of the HD unused, to reduce the distance the read/write heads have to travel. For example, if a regular HD has a platter that the head travels 2 inches on, if you only partition it so the outer inch isn't used, the R/W head only has to move back and forth over 1 inch, instead of two. That speeds up access time, and produces faster performance (firmware, access time, and platter density are the three big things that determine a HD's "speed"). The downside it that you are wasting some of the HD's space, so for most people, I would say that this isn't worth it. Modern drives are so fast nowadays, this isn't needed (at least for home users)
The Samsung is really well reviewed, and Plextor doesn't make their own DVD drives anymore (they are all just rebadged from other makers), they have (IMO) gone downhill from 10 years ago, when their SCSI stuff was bulletproof. Go with the Samsung, Pio, or Liteon.
No, but less voltage=less heat=less risk of killing the RAM. The trade off for higher cost, higher heat, and larger chance of failure doesn't make it worth it, compared to the very minimal speed benefit you gain. Plus, you usually will have to set the RAM's speed and voltage manually in the BIOS (don't know if that's a problem for you).
IMO, the only reason to buy RAM over DDR2-800 is if you plan to overclock, and you think you can go over a 400MHz FSB setting. With the e8400, a lot of them can get up to the 450-500MHz FSB range, so then you would need faster RAM. But I would still look for the lower voltage options within whatever spped you decide on. Going to CAS 4 from 5, or CAS 5 from 6 is insignificant, and only makes you run the RAM at a higher voltage.
Also note if you OC, that 4 sticks of RAM are harder to OC then 2, and usually if the RAM is OK in the first 30 days, it won't die. You can run Memtest to make sure it runs at spec OK.
I like the Corsair 520W, I have it running my Oc'd Q6600 and 8800GT without a problem. Go over to JonnyGuru website for PSU reviews and info. Don't quote me, but I *think* at least some "multiple rail PSU's are actually a single rail, it's just hidden "behind the scenes" as it were. But JonnyGuru will be able to tell you correctly. The people at SPCR are pretty good as well, they won't steer you wrong.