The "usability" is where the marking for false positives comes, so that does need to be considered in the main score.
Performance, not so much, unless so severe that it would change your decision...
Practically, the case of no antivirus must score 12/18 - 100% for performance and 100% for usability.
And would score above Microsoft and Threattrack, only a tiny bit below AVG.
I prefer their scale to that of VB100.
PS. used to be able to get individual results, but all are 404