I did a little research for a friend a few weeks ago who was looking to build a gaming computer for around 1000/slightly more. Through looking through benchmark reports on tomshardware, anandtech, etc, this is some of what I found:
- Core i7, of course, demolished the cheaper AMD phenom IIs. For most tasks (video editing seems to be an exception), AMD gives marginally better bang for the buck. But since your budget is 1000-2000, this doesnt seem like an issue. So core i7 920 definitely seems like the best cpu for the price
- Based on the benchmarks research, the 4890 will handle most current games just fine. The most demanding games, like Crysis, will do quite well with a single 4890, unless youre talking very large monitor, and max res. In this situation, the 4890 looks like it will do so-so. But so-so performance with Crysis is pretty much awesome performance with all other games.
But to get max GPU performance right now, the GTX 295 will give that. From what I've seen, it is approximately equal to a pair or 4890s, a little better than a pair of 4870s. But a pair of 4890s is cheaper. So going with the 4890 you picked now looks good, and then later on, you can just add another one. A single one will definitely give you high end performance for a few more years, and a 2nd one later on should give you high-end a few more years after that.
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Given your budget, for max performance, I would definitely go with 10000 RPM HDDs, as opposed to the 7200 you selected. Another option, given your budget, would be to go with solid state disks.
Pros: Significantly faster for read/write. I havent personally looked at any detailed benchmarks, but I remember seeing an article that stated something like 30% improvement for intensive read/write operations over a (7200 or 10,000 RPM??) SATA. Also, no moving parts, so you don't have the same potential breakdown issue as with HDDs. Also, they are quiet
Cons: Cost a lot more (a few hundred for a large one), and don't come in as high of capacities.
Also, in a few years, they will likely be much cheaper
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RAID configurations (0 or 5) will give you better performance when read/writing from the disk. Of course, this requires at least 3 HDDs, which isn't that big a deal given your budget.
Given your budget, a $300 motherboard looks OK. But there are plenty of high end ones that run $150-200, with the same features. This money could go towards bells and whistles like a monitor, blue ray drives, or solid state disks
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Liquid cooling will also: Look cool, be quieter, and allow more overclocking (if youre into that sort of thing), which can potentially increase performance for intensive tasks by 10-20%. Although, i'm definitely not the guy to go to when it comes to OCing details, but this is definitely an investment that would extend the range of your computer.
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Blue cases are scientifically prove to yield better performance. So blue case, or pay the consequences. 
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Another note: When it comes to components, even with your budget, you definitely want to keep in mind the principle of decreasing return on investment. So for CPUs, for example, for something like a corei7 920 gives you about the ideal performance for your cost. A 500 dollar or 100 dollar model is not going to provide nearlly 2x or 4x the performance.
So even with a high budget, my own preference would be putting the money into monitor, sound, maybe an extra blue ray drive, and other bells and whistles.
With a 2000 budget, you have a lot of room for bells and whistles after getting high-end core components
Sorry, I saw this and just had to comment. As a disclaimer, the next recommendations may be offensive. haha
core i7 demolishes phenom IIs
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yeah, if you take 980GX and put it against an old X3. I don't want to get into this argument, but gaming isn't so processor intensive that you need something like that.
Phenom X4 955 or the Core i5 750 will fit your needs fine...
Moving on to that video card recommendation, this individual must be playing Crysis at 1280x720 with everything set to medium. With most monitors at 1680x1050 or higher, I highly doubt that the old 4 series card will fit your needs. GTX 275/HD 5830 should do the trick.
Okay, the whole RPM issue is also bothering me here. I'm not claiming I'm a tech genius, but 10,000 rpm is just overkill. It's not as if it's not faster, it certainly is: but the thing is, will you ever use it? Unless you handle sustained, intensive data transfer (which does not entail gaming) you won't need it. A cheaper, 7200 rpm drive will suffice.
I once read somewhere that RAID 0 led to strange errors in Windows, but if you want to do RAID 1 or RAID 5 be my guest. Not that it's needed or anything, and the tangible performance increase from RAID isn't "spectacular". No comment on the motherboard, because what he says is true.
No need for liquid cooling, and I'm all for blue cases.
Personal preference time: put money into monitor, gaming mouse, and your actual computer. We don't need to look cool if it will cost us more money, do we?
I could even configure a newegg for you, if you would like.
Edited by L0v3LESS, 07 May 2010 - 11:00 PM.