As I said, the bottom line is actually putting a piece of steel etc on the machine and cutting the damned thing. A proper test piece will exercise the machine in all axes, with internal and external surfaces, circular and flat features etc.

Effects like backlash and machine flex happen when cutting real parts rather than on unloaded machines cutting air. Measure how the test piece compares against the model including circularity, flatness, perpendicularity, dimensional accuracy etc. It would be interesting to hear how the lunchtime legends got on....