Yeah what these guys said.
Looking at it strictly from a gaming perspective, if you keep your video card and upgrade the CPU, you'll see about 25%-30% scaling, which isn't much.
If you go from a 770 (so, a ~4.5 year old video card) to a 1070, you would see a up to a staggering
350% scaling @ 1080p, and
420% scaling at 1440p.
https://www.anandtech.com/bench/product/1731?vs=1768
Going to a 1080, it gets even more ludicrous with up to
415% scaling at 1080p and
540% scaling at 1440p.
https://www.anandtech.com/bench/product/1714?vs=1768
The smallest disparity in benching is a 260% increase on that list. Video card tech is just bonkers when you start going beyond adjacent generations. Even crazier is that modern cards use even
less power on average.