I'm no guru but you'll for sure get more rpm out of your 26 after the install.
Every boat/driver/hull is different but I'd say don't mess with a prop change till you see how she runs after the install. On a side note, be sure to watch your oil temps before and after the install to protect your motor.
Unless you have a VERY efficient bottom and a light load you will probably only go 2 numbers higher on the prop. (depending of course on the boost) Since you probably should have had a 24 before install, I'd say 26 may be just about right with the added horses. More importantly, you'll get out of the hole easier than before. If you are running a Bravo 1 be sure to protect it by rolling the power both on and off and avoid the temptation to slam the throttle in either direction. Best of luck and be sure to give us a report on the after effects.