Building an Upgradable Gaming Rig

Hello, I'm considering a new gaming rig as my current pc is now 6 years old. A part from games, it won't have to do anything fancy. Even then, I’m not too sure what frame rate etc I'm aiming for, I really just want the games to be playable. If I had to give a goal, the new rig should be able to plat Fallout 4 at 50FPS on at least medium settings.

To explain where I'm starting from, my current specs are:
ASUS P5Q-E
Intel E5200 Dual Core 2.50GHz
Zotac GeForce GTX
660 2GB
4GB DDR2
1TB WD Green 5400rpm

And I'm happy enough with the performance on the older Fallout games (3 & New Vegas) as well as Skyrim, Bioshock & RAGE.

My current plan is use my existing peripherals & GPU (Zotac GeForce GTX 660 2GB) and buy a G3258 to over clock. I intend to upgrade both in couple of years. My budget is approx €500. I'm based in Belgium, so I'm using the German pcpartpicker for pricing, but will likely buy from a mix of Dutch, German & French stores. Here is what I have come up with so far, http://de.pcpartpicker.com/p/CbyPTW ,
I can find the mobo for €151 (azerty.nl) and the PSU for €97 (amazon.de) so the build comes to €416 at the moment.

What do you think? Where can this be improved for the best results?

Thanks in advance for your advice.

When do you plan to upgrade? The g3258 will not be able to compete within 2-ish years.

I would recommend a quad core option if you are planning to make it last. Whether its because of lazy ports (I'm looking at you Ubisoft) or because they actually start making more use of multi threaded cpu's, you might be wise to consider a quad core option.

Hi kmnjh & gerkinyagerkin.

I'm planning on upgrading to the i5 4660k or 4670k within 2 years.