I would personally pick something like this:
-a good CPU. While i3's are pretty nice, you can afford a i5. I'd personally pick an unlocked i5 and OC it (although it's more than enough for most tasks at stock speed). A i5 2500K can hit around 4.5GHz.... That's faster than any desktop class Intel or AMD has for sale at *any* price point (including $1000 i7's) for almost any task, and the single-threaded perf would be out of this world. $225 or so.
-a cpu cooler that would support a decent OC. Around $50 or so (I don't keep up with those monthly reviews, you'd have to look)
-a good P67-based motherboard from a decent OEM, preferably with solid state caps, USB 3 and SATA 6Gbps ports, 4 DIMM slots for sure, and ideally that's good at OC'ing, like a Asus P8P67 at $160
-a vid card with great performance at a decent price point (it's all about value). Something like a Radeon HD 6870 around $200 (more than enough for anyone but the most extreme gamers really)
-plenty of decent RAM. Even on an old C2D, 4GB was somewhat limiting for me. 8GB is the min I'd personally buy, but at the current prices 16GB isn't out of the question either (it all depends on what you plan on doing with your PC). In fact, 16GB (4x4GB of decent DDR3 @ 1.5v) should be about $160
-a decent case (solid, good airflow, etc). Being conservative, let's pick an Antec 900, around $100
-a good quality PSU (NOT a no-name cheapo!), definitely 80+ or better, and at that budget you can definitely get something modular too. There's no need for a crazy amount of watts. There's TONS of options out there, but let's pick a very nice Seasonic M12II 520 Bronze ($90)
-a good SSD and a large storage drive. RAID0 setups like you mentioned only help so much for performance. Yes, copying large files (sequential access) is pretty much doubled, but seek times/latency/reading random bits of files all over the place isn't -- that's where the SSD helps. The SSD is faster for starting your OS and apps. Then for the storage drive, speed is not crucial. Something like a 128GB Crucial RealSSD C300 ($240, decently sized for a SSD and still quite fast) and a 2TB WD Green ($80) along with it.
-any decent DVD writer, they're pretty much all around $20
Everything on the above list should come up to $1300 or so. Some people
may will obviously disagree with some points depending on what they do with their PCs. An avid PC gamer would likely get less RAM (no games need that much!) and a faster video card... Plenty of others who don't game much would spent a lot less on the video card and more elsewhere. I think it's one of the fastest (and really high quality) computers you can buy at that price point, without building something with one particular task in mind. Quality parts all-around, super fast CPU/video card, tons of RAM, super fast SSD and lots of storage, great quality modular PSU and everything. It's got it all...
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