I haven’t much looked into what settings affect CPU usage the most because I have a fairly powerful PC but if you’re simply suffering from unstable framerate, you might want to look into stuff like render scale (set this to 100% if it isn’t), anti-aliasing, shadows, all have massive impact on performance while (arguably) not massively impactful on the visual side.
The i3-8100 shouldn’t bottleneck the 1060.
Also worth noting… You might want to look at what your CPU usage is when your PC is “idle” (in desktop right after booting for example). For reference, I have a 4-core CPU (i7-4770k) and my idle CPU usage is 1%… That’s counting Steam, Bnet and Discord running in the background.
Idle means that the PC shouldn’t be doing anything really so if your idle CPU (or RAM or GPU) usage is high, there’s unneeded/unwanted stuff running on your PC.
For those that don’t know, you can check all these in task manager (Windows).