GH I am not that familiar with the race / slalom stuff but most NP is flex top.
The KA and Powerex are generally constant curve, so if used with an NP sail it will not twist enough. However, KA tends to be slightly flexier top so if no using a NP mast and you could only pick KA and P/ex, the KA is more likely to work.
If you are a heavyweight the slightly stiffer top mast may be OK.