A larger frame is more resistant to twisting. A larger frame has a larger sweetspot. A longer frame generates more velocity and therefore more power. The string bed in a longer frame generates more spin due to increased velocity. Thinner string generates more power.
More elastic strings generate more power.
Softer strings, or strings with a softer coating, tend to vibrate less. Thinner strings tend to produce more spin. The more elastic the string, the more tension loss in the racquet after the string job. Although Wilson's research for their Sweetspot string disputes this statement. Tennis Talk - Ask questions or browse tennis discussions.