Good question, with not so simple answer. An i7-4790K + a good GPU will do you some good; however, the cost of a new Ryzen 5 2600 is quite tempting compared to a used i7-4790K. If you don't have a Z87/97 motherboard for overclocking, I say go with a new Ryzen system.
You could start with a new GPU and possibly PSU if you don't have a very good PSU.