Huh??
You upgrade to a slightly faster CPU to get more FPS, then you cap your FPS?
So the game uses 80%. So what? Why is that problem? I would assume that the i7-4790K uses slightly more to do the same job since it's slightly less powerful.
Every game, like any program simply uses the CPU to run the main code. It uses the CPU to:
a) read the program
b) run CPU tasks like AI, CPU-based physics etc, and
c) send draw calls etc to the GPU so it can render the final frames
The CPU will run the code as fast as it can unless:
a) an FPS cap is set, or
b) it slows down because the GPU is saturated
Even when the CPU is the bottleneck it rarely shows 100% usage since most games can't use all cores fully.
So again, I'm CONFUSED on what the problem is. Just leave your CPU alone, and leave the game uncapped. A lot of people run the game at 250FPS+ as that seems to enable VSYNC OFF (more responsive) and the high, relative FPS can make the screen tear not be obvious.
OTHER:
If you have a CPU fan noise issue then you need a better CPU cooler and/or adjust the fan profile. Can't think of another issue that you might be concerned over.