The interest is to find out what the standards of widebody design are, and pick up where the differences are. Note that although the length of widebodies are wildly different (from 46 m of A310 to over 75 m of A340-600), wingspan differs hugely (from under 44 m of A310 to almost 80 m of A380) and engine arrangements also differ, the heights are similar.
Especially striking is how the underbellies of various widebodies have just about the height for 163 cm headroom, and not more.