Games do not use Hyper Threading so for a gaming rig there is no reason to buy an i7 over an i5 CPU. The money saved can go towards a graphics card.
The Intel HD 4000 has about 85% - 90% the performance of a Radeon HD 5570. That means the Intel HD 4000 can outperform a Radeon HD 45xx graphics card.
Crysis 3 seems to be the exception to that rule as it likes more cores. OP already has the i7, apparently. The most important thing here is what is the PSU in the system and how much can they spend.