It really depends on which i5 and which i7. Make sure you're comparing comparable models. But in general, an i7 is a faster processor than an i5. If you do compute-intensive tasks, particularly ones that make good use of multiple threads, you will see a great increase by bumping up to an i7. If you are just surfing the Web, word processing and gaming, the i5 will fit the bill fine. As long as your CPU isn't slow enough to be a bottleneck, the graphics card defines your gaming experience.
But in the end, if you can get an i5 and an i7 for the same price, why not get the better model, if for nothing more than a bit of future proofing?