Hey. I know it's confusing...
The AMD has four cores, but each of those cores is WEAKER than the Intel's by roughly 40%. If we consider StarCraft 2 for example, it only uses two cores so it runs best on the Intel CPU. SKYRIM uses a bit more than two cores but still favors the G3258. A game like Battlefield 4 is probably going to run better on the AMD CPU so it's not a straight answer.
Games also have an AVERAGE frame rate and a LOW frame rate. The AMD CPU is more prone to have a LOW frame rate. Let's say a game gets the same average frame rate on both, however the AMD might dip below 20FPS more than the Intel which causes periodic stutter (there are other causes of stutter).
My understanding is that currently MOST GAMES will run best on the Intel G3258.
OVERCLOCKING:
It's not too hard. I suggest you wait and investigate that once you have your system but I'd run it for a while to make sure it is stable. I personally just use the "XMP" setting so all I did was the following:
1) Bootup into BIOS ("DEL" key on boot)
2) Find CPU section, choose "XMP" setting and SAVE
*Please note that not all motherboards support overclocking. The board you chose does and looks like a good value and fairly solid board (Z97 Asrock).
Summary:
Both the systems you designed are fairly good and as I said there are Pros and Cons to either choice. Personally, for the reasons I stated I'd get the G3258 setup.
And the graphics card I recommended again because it supports MANTEL and the free games.
Update:
I forgot to mention the Intel CPU puts out a lot less heat, and the CPU fan shouldn't be as noisy either. You'll still want to setup a fan profile using the motherboard fan control software.