I will start up front with - anything you test on a different material than your final material will likely be wasted testing…wood varies so much.
That being said, these are some comparisons of the different settings options that might prove helpful:
and this is a fabulous write-up on how to prep your photo for engraving (even if you don’t use Photoshop) - because if it looks great as a digital file, it likely won’t look great after engraving: