Alright, so a couple notes:
You still didn't give us the budget. I'm assuming the 8-core you were referring to is the AMD FX-8350 (125W TDP, 4 GHz). That's currently running at C$190. A decent motherboard pairing for this is something like MSI's 970A-G46, that's another C$70. Also, with that Vishera FX's 125 W output, I highly recommend ditching the stock cooler in favor of a CoolerMaster Hyper Evo 212 or similar. If you decide to throw in extra money and get a new PSU, that'll even allow you to overclock that thing some. With a case, you're looking at a roughly $330 expenditure. So what else can you get with that money?
Well, the bare minimum AMD-based configuration I described above will look something like this:
http://pcpartpicker.com/ca/p/xA0V and comes to $340. You can wiggle that around +/-$10 depending on which exact case you prefer.
What would be another comparable configuration for the same price? Well, due to a current combo discount, you can get this i5-3470 based build:
http://pcpartpicker.com/ca/p/xA5I for $270, where apparently Newegg is willing to give you an ASUS board for free. Failing that, this
http://pcpartpicker.com/ca/p/xA8T build, at $320, is more comparable to the original Vishera-based build.
Now, I'll address how these builds achieve your stated goals: (1) best value for money and (2) longevity.
(1) They're both strong performance for the $320-330 price tag. You'll notice a significant improvement in both of them, and both will likely provide you with a good experience in any modern title. However, the i5 will be slightly better in most titles, and in the case of PS2, much more noticeably so. Since you're building this exclusively for gaming, the extra 4 cores of the FX-8350 won't translate to the same performance benefit they do under more productivity-oriented tasks.
(2)You are unlikely to want to upgrade the CPU of either of those systems for at least the next 12 months. It's difficult to predict what might happen beyond that, but I will say this: back in 2010, I built a Phenom II x4-based system, and did not feel it needed ANY upgrading at all until PS2's beta came about. That's a solid 2 years from a gaming rig, and I consider that pretty good longevity. So the fact that you will pair your new CPU to a 660 is likely to duplicate that experience for you.
But the situation is a little more complicated now. Chiefly among these complications are these factors:
- The FX-8350 is overclockable, but it already consumes considerably more power than the i5, and that power requirement will only go higher, as will the heat output. The extra heat sink I suggested will allow you some overclocking headroom, but if you're interested in pushing it's performance higher, you'll need both a new, quality PSU and an even better CPU sink (perhaps even closed-loop liquid) to truly make a noticeable difference. That's at least another $150 on top of the stated cost.
- AMD970 chipset supports SLI and crossfire, but lacks PCIe 3.0x16 (which your 660 is already capable). That means expanding the graphics horsepower of this rig in the future would be better accomplished by SLI'ing a second 660, but given the CPU's high power requirement, a beefier PSU may be warranted. This increases the cost of your next potential upgrade.
- The i5 is not really overclockable. This means its power output is much more predictable, and crucially lower, so you don't have to worry about getting a new PSU, even if you swap the video card later (see below). This also means that the i5 will run quieter, especially if you also get an aftermarket heatsink for it.
- The i5-based rig DOES have PCIe 3.0x16 support, but unless you grab the combo that gives you that ASUS mobo for free, you are unlikely to get worthy SLI/Crossfire support. So this means upgrading the graphics on this platform is better achieved by buying the next-gen card that can fully tax the single PCIe 3.0 slot.
- The i5 really can't be upgraded much if you decide to try to do so in the future. An i7 would fit in its place, but it won't improve performance as much as it increases the price. Haswell (Intel's next-gen architecture due to come out sometime this summer) probably won't use the same CPU socket, so those new chips won't be compatible either. The FX on the other hand may be upgrade-able further still when AMD's next-gen stuff coms out, although socket AM3+ has been around for a while, and I don't really know when AMD plans to put the next big thing on the shelves.
Given all this, you basically have a choice between:
1. A noisy space heater that allows you to make it a more efficient space heater.
2. A slightly less noisy space heater that you really can't modify much in the future but that performs better now.