Which is predicted to have the shorter sulfuroxygen bonds: a sulfite ion or a sulfate ion?

The sulfate ion should have shorter sulfur-oxygen bonds than a sulfite ion.
The sulfite ion is a hybrid of three equivalent contributing structures.
The bond orders of the ##S-O## bonds in any one contributor are 2 1 and 1.
The bond orders of the ##S-O## bonds in the hybrid are an average of these numbers.
##BO = ##2 + 1 +1)/3 = 4/3 = 1.33
The sulfate ion is a resonance hybrid of six equivalent contributing structures.
The bond orders of the ##S-O## bonds in any one contributor are 2 2 1 and 1.
The bond orders of the ##S-O## bonds in the hybrid are an average of these numbers.
##BO = (2 + 2 + 1 +1)/4 = 6/4 = 1.50##
The greater the bond order the shorter the bond length.
The ##S-O## bond order is greater in the sulfate ion so sulfate ions should have shorter ##S-O## bonds.
Experiments confirm this prediction.
The measured ##S-O## bond lengths are 149 pm in sulfate ion and 151 pm in sulfite ion.