Depends on what price you are getting the i7. If you get it around $100-$150 used, then its still good value. It is still a good chip for gaming. But be careful when buying used, as most of the unlocked chip users are first timers, and usually these unlocked chips end up abused. Do lots of stress test before pulling the plug.
No point buying new, as it will cost you a fortune...
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel - Core i7-4790K 4 GHz Quad-Core OEM/Tray Processor ($531.10 @ Amazon)
Total: $531.10
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-01-08 00:43 EST-0500
Instead, you can get this...
PCPartPicker part list /
Price breakdown by merchant
CPU: AMD - Ryzen 5 2600 3.4 GHz 6-Core Processor ($164.89 @ OutletPC)
Motherboard: ASRock - B450 Pro4 ATX AM4 Motherboard ($61.00 @ Newegg)
Memory: Corsair - Vengeance LPX 8 GB (2 x 4 GB) DDR4-3000 Memory ($68.99 @ Newegg)
Total: $294.88
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-01-08 00:44 EST-0500
It will give you mostly better or similar performance... https://cpu.userbenchmark.com/Compare/Intel-Core-i7-4790K-vs-AMD-Ryzen-5-2600/2384vs3955