Start with one change
A different layer height can make a surface comparison hard to interpret. So can changing flow, temperature and speed together. Keep a copy of the original profile, change one relevant setting and compare the same feature.
Use a small specimen when the question is narrow. There is little reason to print a whole tray of parts just to inspect a seam or the top of a curved surface.
What the ramp and sphere are for
The ramp puts layer steps on a simple 45° slope. The sphere changes the surface angle gradually, showing how the finish changes near the crown. Compare the actual sliced time as well as the photographs.
A finish that looks better close up may be worth the extra time on a display piece and irrelevant on a hidden part. Neither outcome requires one setting to be declared best for everything.
Changing nozzle size
Check the printer, hotend and material compatibility before replacing a nozzle. Use the correct machine profile and slicer settings for the fitted size. A nozzle comparison should identify the size, layer height and line widths rather than attribute every difference to the nozzle alone.
Keep the main filament comparison consistent
The published Copymaster setup used a 0.4 mm nozzle and 0.20 mm layers. Any later settings experiment is a separate test. Its result should not silently replace the original one in a product comparison.