In high school (8 yrs ago)..., I played high F# and G (above High C) Consistently, but now my max is about High E above High C... I need to practice...
I have a Double High C Method book by Frank Minear... It works. (I just don't have time to play anymore)... Frank played with Stan Kenton for a while... He's gone to heaven, but his son is my friend and gave me his personal method study book.
In my junior year, I hit the G above high-C, but now I'm playing the F-F# pretty consistantly. It all depends on how I'm feeling. Playing high is dependant not only on ones own ability (but that will be the limiting factor to yur max), but also on whether or not you believe you can play that high.