Hi!
You would not probably gain more speed!!!
Old style 11x7, 11x7,5 and 11x8 " props suits "old style" (fast flying) pattern planes like the Hanno Prettner "Curare" and such.
For more modern (larger, with lighter wing loading) pattern planes that flies slower, larger APC props work best.
Soo ...What plane do you have???
Remember also that if you put on a larger prop you have to lengthen the pipe (trail and error process).