If you want to update from an overclocked G3258, you have about 4 choices:
haswell or later unlocked quadcore i5
haswell or later unlocked quadcore i7
haswell or later unlocked sixcore i7
haswell or later unlocked octacore i7
No seriously, if you want a true update to your cpu, you need one with the same single core performance or better, which is only another haswell(or later) cpu with the same Ghz or higher.
If you would upgrade to a 3 Ghz i5, i think you might get situations in Dolphin where the old cpu was faster. Having more cores than 2 does help Dolphin, but not that much.
haswell or later unlocked quadcore i5
haswell or later unlocked quadcore i7
haswell or later unlocked sixcore i7
haswell or later unlocked octacore i7
No seriously, if you want a true update to your cpu, you need one with the same single core performance or better, which is only another haswell(or later) cpu with the same Ghz or higher.
If you would upgrade to a 3 Ghz i5, i think you might get situations in Dolphin where the old cpu was faster. Having more cores than 2 does help Dolphin, but not that much.