You will see very good improvements when upgrading from i5 to i7. Approx 50%, which is a very good improvement when you have a heavy card like the 2070. The i7 4690K is approx 60% better than the i5 4690.
Mind that the i7 4790k does not come with cooler. You must be buying the used CPU, so just check for good CPU cooler too.
Please also do share your full PC specs. What resolution you play at?