  We prove that the signature bound for the topological 4-genus of 3-strand
torus knots is sharp, using McCoy's twisting method. We also show that the
bound is off by at most 1 for 4-strand and 6-strand torus knots, and improve
the upper bound on the asymptotic ratio between the topological 4-genus and the
Seifert genus of torus knots from 2/3 to 14/27.
