"The difference between Cr−Cr quadruple and quintuple bonds is not just another weak δ bond."
This is very nice study to find some correlation between several bond metrics, ligand types etc. and the M-M bond distance and bond order. As you can imagine, for some systems, there IS nice correlations. For example, systems like Cr2L4, weaker Cr-L interactions yield to stronger Cr-Cr bonds. I found this paper very useful to design new ligands to maybe break the record short distance and discover some unique properties.