The best way is to try it out and see for yourself since you already own it. But the 4790 k is much more powerful than the 975, it's not just because of the extra clock speed, but also the 4 generation difference that gives it like 40% more power per ghz. And the fact that you can use higher frequency ram.
But your current i7 should still be good for the uses you mentioned, it might run into some problems with the latest cutting edge games, but it will be fine for moderate games.