depending on the game whether or not it is very cpu intensive. If you play games such as bf4 64 person multiplayer, star citizen, gta 4 or anything with a lot of AI, the i3 will bottleneck your gpu. But in games that require more gpu horse power such as bioshock infinite, far cry 3, etc, the i3 will run absolutely fine.
This is for reference:
https://www.youtube.com/watch?v=evXpqpNhu_Y
There are some benchmarks for a dual core pentium (which your i3 will outperform) vs an i7. So you can expect similar performance.