That depends on a lot of parameters. Which GPU do you want to buy ? Which CPU are you much interested in ? What's the Screen RES of your MONITOR ? Are you a casual or Hardcore Gamer ? There has to be some balance made between the two...... We cannot pair a WEAK CPU with any high-end flagship GPU, and vice versa.
It will bottleneck the card. Also, if suppose you have a very powerful CPU, but paired with an entry-level GPU, then this combo is bad as well. What's your budget for this upgrade ?