IPC improvement from 2nd to 4th generation in somewhere between 5-10% at best depending on load. If OP happens to be in CPU bound situation he may find that expensive i7-4770k gives like 6% fps boost in games. 98% of games will perform on 2600k vs 4770k exactly same on 4.5GHz. As that gives performance above what games today need unless OP gets very strong multi GPU setup. There is quite higher improvement in memory dependant situations as 4th generation has considerably higher memory throughput. (not games, just very few special applications) And if multi GPU setup is in question, then another difference between 2nd and 4th gen which may matter is PCIe 2.0 vs 3.0, that gives in games up to 4% difference in 2-way SLI/CF. As he can have 2600k for free, I say, it is good upgrade over 1st gen i5.