We describe a CPU bottleneck as when you're playing at default graphics settings and the games aren't running fullspeed. If you increase the IR/AA/AF beyond default and it starts to slowdown, then yes, you are correct in saying that you have GPU bottleneck.
You first post has some confusing grammar, so I was thrown off by it.
Just so you know, Twilight princess is a demanding game when you get later into the game and hit Hyrule field, and I believe that even an overclocked i5-4670k has issues with it.
The only thing a GPU upgrade will do for you in Dolphin is allow you to raise the enhancements farther. Games won't run faster, they'll just look nicer.
If you do want to do a CPU upgrade at some time, the i3-4130 and i3-4340 will be faster than an i5-3570K
You first post has some confusing grammar, so I was thrown off by it.
Just so you know, Twilight princess is a demanding game when you get later into the game and hit Hyrule field, and I believe that even an overclocked i5-4670k has issues with it.
The only thing a GPU upgrade will do for you in Dolphin is allow you to raise the enhancements farther. Games won't run faster, they'll just look nicer.
If you do want to do a CPU upgrade at some time, the i3-4130 and i3-4340 will be faster than an i5-3570K