You'll want to get a 4th gen i3-4130 or i3-4340, as they have at least a 30% increase in speed over Ivy Bridge in Dolphin benchmarks.
Dolphin relies more heavily on the CPU than the GPU, so you were most likely getting bottle-necked by the old i3, not the HD 5450
Dolphin relies more heavily on the CPU than the GPU, so you were most likely getting bottle-necked by the old i3, not the HD 5450