Finalizing a Build

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1

I picked the parts for this build a couple months ago, but I wasn't ready to build it at the time, as I was going to save it for my senior project in high school. I saved the PCPartPicker link to the build because I knew I would need it again. (I have an optical drive that I can use.) 

http://pcpartpicker.com/p/4L3VGX

I'm asking a couple things before I decide.

1) If I were to upgrade any part of this build, what would be the order I would do it and what would it be? I may be willing to go over budget a little if I'm ~$50 from a way better part. Upgradability is a requirement for this build, and as a newbie, I don't know what is out there or what the next-up part is. If a build that is only $300 shy from killing this one, I'd be willing to spend the extra cash. I hope you understand what I mean. With that said, I was looking at an i5 processor and possibly a R9 280 or R9 280X if it will really perform well enough to justify the price increase.

2) With it being a couple months old, is there any new hardware that I should look at? This question could tie into the first.

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I think an I5 and a 280x would be well worth the  money up front and you can focus on cooling and storage upgrades.

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R9 290 + i5 will max probably just about every game for a couple of years or so. The 290 is one of the best bang for buck cards, and the i5 is one of the best gaming CPUs on the market and is only outclassed by i7s in specific titles optimized for more than 4 threads.

That does end up being substantially more though: http://pcpartpicker.com/p/HdkXVn

And of course ideally you'd want the 4690k and a Z97 board so that would add on probably another $75 or so

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So an i5 is looking like what I'm going with. Now, an R9 280, 280X, or 290?

Are the price differences proportionate to the performance differences? I know it's hard to say exactly, I'm mainly talking like a obvious choice of one over the others. Or like I said, do they all have the same value (I'm talking actual value, not price)?