Can you not analyse the numbers you provided me?
No, the processor is not a god. But for a gaming rig its pretty much the strongest budget CPU that has a seriously viable future upgrade path. With AM3+ your limited to what is out now, a processor that just about punches with an i5. A 'big upgrade' down the line is likely a new mobo, CPU and DDR4 ram. Which will be a costly adventure.
In the long run, living with the pentium and upgrading to a more powerful processor when the funding allows is a much better, cheaper long term investment. With the GPU that'll sit in this budget, something like a 280X, the Pentium will only have a few instances where is doesn't quite match, and FC4 being a rarity where a quad core is required.
As for your overclocking reference. That showed at least 10% increases...? Anyway, performance gains would be marginal because the processor isn't even struggling with the game in the first place. Not even a G3258 'stuggles'. But due to how threading actually works, a G3258 would gain more in gaming from OC'ing because more processing threads are being loaded into less cores.
That metro benchmark says two things. There is a very good increase (~20%), on a game that is one of the toughest out there, using a card that is powerful enough to see a CPU bottleneck. And that is against an i7. Is 50fps average not enough? OCd into the 60s average? Do you need to spend another $100 for ~10fps, or $250 on an i7 for ~20fps, where you TV/Monitor is more likely to be 60Hz... but my reference was in terms of single thread performance, ie, most non-specialist software scenarios.
Sweclockers are pretty damn respectable. They have a very grounded opinion, in fact say even the G3220 is better 'value for money'. Look carefully at the results.
But all the tests on that site are a stock CPU. There is a separate section for OC'd. Its nothing to snuff at. It runs every game perfectly fine. A G3258 OC in scenarios matches a stock i5K, in some matches even that of an OC'd i7K and in others where it suffers isn't so much that its 'bad', its just not as good as a processor 2x or 3x more expensive.
Say what you want on the mobo front, but it offers a significant OC potential for a 'novice', at the cost of just getting a better deal on the RAM he choose. Asus ones start at ~$95 on Newegg, he was already paying $80. Sure drop to a B85, but be prepared to see someone well over their head doing it manually. OC'ing the Pentium can see a 20% increase in many cases.
TLDR is investing in a i5 + 270 over a G3258 + 280X, for a gaming machine is a waste of money. Your putting money into untapped resources. But the future upgrade favours replacing the CPU for an i5+ over a new GPU that is better than a 280X. With Skylake on the horizon, a deal can most certainly be had too. Even an FX-8350 couldn't keep up with a 'stock' G3258 in gaming, apart from Metro in those benchmarks. And its not like the Pentium couldn't play it at 1080p ultra at respectable fps. So much for an extra $100 in a 'gaming' machine, that only really makes a minor difference in the toughest of AAA gaming. Go to the big PC games and it won't even make a difference.
We want to see new PC gamers being blown away at the difference, with the most cost effective future proofing. The G3258 is just that.