dipeshtp2,
On behalf of Tom's Moderator Team, welcome aboard!
Since Intel significantly changed their processor lineups for 8th and 9th Generation due to the "Core Wars" with AMD, there is no direct equivalent to the i7 4790, which is still a potent Quad Core gaming processor. The newest equivalent processor is the 7th Generation i7 7700, but I seriously doubt whether you'd notice any difference in gaming performance.
The specifications are very similar between the 4790 and the 7700, and the modest increase in IPC (Instructions Per Clock) from 4th Generation 22 nanometer processors to 7th Generation 14 nanometer is nothing to get excited about.
i7 4790 - https://ark.intel.com/products/80806/Intel-Core-i7-4790-Processor-8M-Cache-up-to-4-00-GHz-
4 Cores / 8 Threads
Base Clock 3.6GHz
Turbo Boost 4.0 GHz
i7 7700 - https://ark.intel.com/products/97128/Intel-Core-i7-7700-Processor-8M-Cache-up-to-4-20-GHz-
4 Cores / 8 Threads
Base Clock 3.6GHz
Turbo Boost 4.2GHz
In addition to your processor, you would need to replace your motherboard and memory with DDR4, which together is a considerable expense for just a few more Frames Per Second that you won't notice. Your existing 4790 will support a high end graphics card, so that's where I'd put my gaming upgrade money.
As an alternative, if you have a Z87 or Z97 motherboard, you can upgrade to an i7 4790K, a good air cooler, and overclock the processor. Even without overclocking, the "K" variant has noticeably better performance:
i7 4790K - https://ark.intel.com/products/80807/Intel-Core-i7-4790K-Processor-8M-Cache-up-to-4-40-GHz-
4 Core / 8 Threads
Base Clock 4.0GHz
Turbo Boost 4.4GHz
Most 4790K's will easily overclock to 4.6GHz, while some overclock as high as 4.8GHz with high-end air cooling.
If you don't already have an SSD, that's always an excellent upgrade. It'll vastly improve boot time, overall system responsiveness and significantly decreases game loading time which makes your PC feel like a new rig.
Once again, welcome aboard!
CT