guys this is all great advice! wise words from John too.
i can see how everyone's approach is different and not necessarily better than the other.
having said that i think it'd be wiser not to start experimenting with a decca tree seeing how i won't have much time to set up, which is really limiting my fun.
so the new alternate option would be:
XY coincident pair of LDs above conductor's head aiming at the orchestra- gving me a strong center
ORTF pair of SDs (would AB make more sense here?) on the choir - for more stereo effect
anyone please feel free to tell me this sucks or not, and why.
in any case i'm gonna have a great time (keeping fingers crossed and asking for more advice on GS

)
Regis