4790K is not "better " than the 7600K. but it is not far behind it in power. why sometimes its worth getting one if the price is right...
in usa 7700K is 379.99, and 4790K is about 279.99, if you had to buy both with motherboard and memory, its a close call on price.
and future expansion, and new motherboards have more PCIE paths then older ones (20 versus 12) making system run smoother.
so its not just cpu versus cpu, its cpu/mobo/ram versus cpu/mobo/ram. a 7700L with a Z270/32GBram 3200 will run a lot faster than a 4790K with Z97 and 32GB 13333, its just a matter of deciding if that 10-20% less power is needed or not