The ornamental design for a performancesock, as shown and described.
FIG. 1 is a perspective view of a performance sock showing my new design;
FIG. 2 is a right side view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a front view thereof; and,
FIG. 6 is a rear view thereof.
The dot dashed broken lines at the collar of the sock in FIGS. 1 and 6 depict the bounds of the claim. The even dashed broken lines on the top of the toe and ankle portions of the sock in FIGS. 1-4 and 6 depict stitching and form no part of the claimed design.