I'm not sure if Rogue Squadron II/III actually work properly, even with a fast PC. If those 2 games are important to you, you might want to do some research on them. Mario Kart, Wind Waker and Smash should run fine with the discussed cpus, but i'm only 90% sure of it.
I want to give some input on the G3258 specifically. Keep in mind that it only has 2 cores, with no hyperhreading, so only 2 threads. If you are planning on getting a G3258, you should look up the prices for i5-4670K, i5-4690K, i7-4770K and i7-4790K, you might get lucky on one of those. Or, if you don't want or can't overclock, one of those without the K. The K and non K variants are virtually the same performance, if you don't overclock. All of those should fit into the same mainboards as the G3258 and they are all upgrades over the G3258. The extra cpu cores help a bit with Dolphin(which actually maxes out at 3-4 cores i think), if a game can use the dual core setting, so not all games and even then it's not enough to justify spending a lot more money.
The G3258 with only 2 cores would allow you to play some older pc games, while the i5 and i7, would allow you to play more regular pc games up to one level below games like Shadow of the Tomb Raider, if you get a GPU with enough performance. Shadow of the Tomb Raider could maybe run ~30-40 fps with the i5 or i7, if your GPU is fast enough(at least that's what i got with an i5-4670K + GPU). Witcher 3 is an example that would run with a i5 or i7 combined with a proper GPU, where the G3258 would give you some trouble.
The integrated graphics of the G3258, i5 and i7 do not appear to be much different. If i'm reading this correctly, the i7 iGPU is just "up to" 8.7% faster than the i5 iGPU, and the G3258 iGPU and i5 iGPU seem to be the same. So the difference in the iGPU between those would not justify spending more money. Paying more for the i5 or i7 would make more sense, if you also get a proper GPU. If you want to use integrated graphics of the cpu, then, like Nintendo Maniac 64 already said, RAM speed matters. The faster the RAM, the better, and 2 sticks is a requirement. If you use a proper GPU, it's more ok to use slower RAM and spend a little more on other things instead.
I want to give some input on the G3258 specifically. Keep in mind that it only has 2 cores, with no hyperhreading, so only 2 threads. If you are planning on getting a G3258, you should look up the prices for i5-4670K, i5-4690K, i7-4770K and i7-4790K, you might get lucky on one of those. Or, if you don't want or can't overclock, one of those without the K. The K and non K variants are virtually the same performance, if you don't overclock. All of those should fit into the same mainboards as the G3258 and they are all upgrades over the G3258. The extra cpu cores help a bit with Dolphin(which actually maxes out at 3-4 cores i think), if a game can use the dual core setting, so not all games and even then it's not enough to justify spending a lot more money.
The G3258 with only 2 cores would allow you to play some older pc games, while the i5 and i7, would allow you to play more regular pc games up to one level below games like Shadow of the Tomb Raider, if you get a GPU with enough performance. Shadow of the Tomb Raider could maybe run ~30-40 fps with the i5 or i7, if your GPU is fast enough(at least that's what i got with an i5-4670K + GPU). Witcher 3 is an example that would run with a i5 or i7 combined with a proper GPU, where the G3258 would give you some trouble.
The integrated graphics of the G3258, i5 and i7 do not appear to be much different. If i'm reading this correctly, the i7 iGPU is just "up to" 8.7% faster than the i5 iGPU, and the G3258 iGPU and i5 iGPU seem to be the same. So the difference in the iGPU between those would not justify spending more money. Paying more for the i5 or i7 would make more sense, if you also get a proper GPU. If you want to use integrated graphics of the cpu, then, like Nintendo Maniac 64 already said, RAM speed matters. The faster the RAM, the better, and 2 sticks is a requirement. If you use a proper GPU, it's more ok to use slower RAM and spend a little more on other things instead.