Background Tennis racket string tension may influence ball speed, directional control, and perceived comfort, yet evidence from real hitting tasks remains limited. Objective This study examined the effects of five string tensions on forehand and backhand performance and tested whether subjective comfort aligns with objectively optimal tension. Methods Twenty-seven trained tennis players completed a repeated-measures experiment using five identical rackets strung at 40, 45, 50, 55, and 60 lb. Ball speed was derived from high-speed video, accuracy was scored using a concentric target, and perceived comfort was assessed using a 5-point Likert scale and final preferred-racket selection. Ball speed and accuracy were analyzed using 2 hitting sides × 5 string tensions × 2 sex groups mixed-design ANOVAs. Correlations examined associations among fastest racket swing speed, subjectively preferred tension, and individualized optimal-tension outcomes. Results Forehand ball speed was significantly higher than backhand ball speed, F (1,25) = 41.51, p < 0.001, ηp 2 = 0.624. String tension did not significantly affect ball speed, whereas accuracy differed significantly across tensions, F (4,100) = 40.37, p < 0.001, ηp 2 = 0.618, generally improving at higher tensions. A significant tension × sex interaction was also observed for accuracy, F (4,100) = 4.22, p = 0.003, ηp 2 = 0.144. Fastest racket swing speed was positively associated with ball speed at the speed-optimal tension for both strokes, but not with optimal-tension values or best accuracy scores. Subjectively preferred tension showed limited agreement with objective speed- or accuracy-optimal tension, and no correlations remained significant after FDR correction. Conclusion Within 40–60 lb, string tension influenced accuracy more consistently than ball speed. Perceived comfort provides complementary information but should not replace objective performance testing in individualized racket configuration.