To set launch options, right-click Hell Let Loose, and select properties. From there, select set launch options. -refresh [monitor refresh rate] -USEALLAVAILABLECORES -malloc=system
For the refresh rate, set it to your monitors refresh rate. Ex. -refresh 144 -dx12 is an optional launch option, and will boost your framerate quite a bit, but can cause issues with crashing, particularly on Foy. If you use this, make sure to set your screen mode to windowed fullscreen in-game before adding this launch option, or your game may crash or refuse to start. Also, do not alt-tab when using dx12, as it may also make the game crash.
These are personal preference, but will give you a decent boost to framerate without sacrificing visual fidelity. V-sync is particularly up to you if you want to enable it or not, but in my experience, I run it in tandem with G-sync, so there is no noticeable mouse delay, and it keeps the framerate steady.