Largest system studied by full CI
FCI of N2 with about 10^10 CSFs must be the largest such calculation...

Ref:
A full-configuration benchmark for the N2 molecule, 
Elda Rossi, Gian Luigi Bendazzoli, Stefano Evangelisti, Daniel Maynau, 
https://doi.org/10.1016/S0009-2614(99)00791-5