Yet another balancing act. Too little overlap and your infill does not connect to the perimeters, resulting in a weak print. Too much overlap and you will get artefacts in the walls of your print as you over-extrude at the end of each infill line, meaning the next perimeter gets distorted.
For this I'm just going to give you guidance on the principles, the test STL used isn't that important (I often use the Mobius plate test piece for this).
Remember that your top layer is no longer representative of the rest of your print - you've just meddled with the flow ratio. The critical aspect here is to get (on all layers other than your top layer) a good connection between infill and perimeters without causing artefacts on your outside walls. The ideal aspect is to do that whilst getting a perfectly filled top surface.
Personally, I have tiny holes in some of the infill/perimeter joins on the top surface - I get a really nice smooth top surface and since this only affects the top layer it doesn't bother me. Not for you? That's fine, have a slightly higher overlap and get zero gaps but a slight ridge on the top layer, but beware you don't cause artefacts on the lower walls!
Told you it was a balance...