I'm glad I confirmed this info.
This means your machine has 8 physical cores with 16 logical processors, meaning it's hyperthreaded.
ANSYS solvers are already CPU intensive, so hyperthreading actually can degrade the solver performance. I strongly recommend to disable hyperthreading (best to do it in BIOS level, find online instructions for details). Then, solve with up to 8 cores.
"Use automatic settings" is always recommended, to just let the solver determines how to distribute jobs. There is a rare circumstance where automatic doesn't work well and you have to manually specify these settings. If you see simulation unexpectedly, extremely slow, or just hang/abort, you may need to a manual way, which should be discussed with HFSS expert on what settings to use for your particular simulation.
Your graphics card is good and the setting to use GPU is fine but the use of GPU/GPGPU is very specific to certain analysis type. The solver will automatically determine if GPU can be used. If you want to know details of which analysis/simulation can benefit from it, you can try asking on the other section for HFSS questions.