Assuming both 4th and 5th generation Core i7 has the same clockspeed, the 5th gen should have slightly better performance. The average performance increase from 4th to 5th gen is about 4%. That means a 5th gen Core i7 running at 3.0GHz would be about equal to a 4th gen Core i7 running at 3.12GHz... Not a big difference.
The biggest performance increase is actually in the integrated graphics core. The 5th gen Intel HD 5500 is roughly 15% more powerful than the 4th gen Intel HD 4400 on average, but that varies depending on the game. It may not be much but it is definitely better than the meager 4% on the CPU side.