I don't have any first hand experience with WIN 231, but I consulted two of my loading manuals and in the Hornady book, you're already close to their max. Either way, both of them showed a maximum velocity of only about 1100 fps.
If you want better performance, they you'll want a different, slower burning powder. This one is too fast for your application. I've used Power Pistol and Accurate Arms No.7 with good resutls. Although my powder puff loads in 9mm tend to be with Bullseye.
Hornady recommends Power Pistol, Winchester Action Pistol and Accurate Arms No.7.