Depends on the resolution and the graphics card that you will be choosing...
For very high resolution gaming with Full quality settings turned ON along with powerful cards such as the HD 58xx series, the i7 8xx are better matched...
But even the i5 is no slouch...It can also handle them well but in some cases, you can see it lagging behind...
So if you are tight on budget and want to include a powerful card, then you can go with i5 in order to divert the funds to the GPU...