Of the three builds so far, two are for amd FX based builds.
There are two problems with FX as I see it.
1. Few games can use more than 2-3 cores making 6 or 8 cores useless.
2. More importantly, the FX architecture is slow per core, and you will have no upgrade past overclocking the devil out of your chip.
My suggestion for an expandable build has a couple of elements:
1. For gaming, start with a good quality strong psu, in the 600-650w range
That will allow you to upgrade in time to much stronger single graphics cards. It could handle a card as good as today's GTX780ti. Look at a Seasonic psu, arguably one of the best quality brands.
2. You need a motherboard with cpu expansion capability. Today, that means to me any Z97 based motherboard. It will handle a entry level $75 G8358 dual core, a i5 quad core, a i7 4790K, and is compatible with future 14nm broadwell.
For gaming, the graphics card is all important. My rule of thumb is to budget 2x the cpu cost for the graphics card.
With a combined budget for cpu and gpu of about $450, I would divide it this way:
cpu i3-4350 @140
gpu GTX760/770 or R9-280/280X which will be in the $260 range.
The i3 is a dual core with hyperthreading, giving 4 dispatchable tasks. It is an effective gamer.
The graphics cards are similar performers, benchmarks do show differences, but actual gameplay will be similar.