According to this lovely guide by Inri from Mabinogi World,
Mabinogi Generations, party performance comes out in G6S1. However, that guide is based on other versions of Mabi so who knows when it will be implemented in NA. It's definitely not available now and G6 is quite a long ways away, but it could be implemented earlier.
Why don't you create party scores now anyways? You can't play them in game but at least they'll be ready to use.