CPUs don't bottleneck GPUs, CPUs bottleneck software. If you want 60fps in a game, and a CPU can only deliver 50fps, it doesn't matter what GPU you have, fast or slow.
An i3 will deliver a good experience in any modern game, but just like any CPU, you'll find scenarios where your maximum framerate is limited by the CPU. I expect the i3 will provide you with a good enough experience, though the i5 would provide you a better one. If the i3 is good enough for your expectations, there's no need to spend more on an i5.