A Winners Choice string might give you a couple FPS but not much. 261 FPS isn' t too bad with you only having a 28.5" draw length.
There are only a few ways to increase speed.
1) increase draw weight (doable)
2) increase draw length (not a good idea)
3) decrease arrow weight (you don' t want to)
4) get rid of or use lighter stuff on your string
5) make sure that your cam is set at it' s optimum rotation