Hi Ben
Normally a large choir should be seen as on instrument (for recordings). It also is not imortant to make out each single voice - no, the opposit is the aim. So one should use the A/B stereo configuration. If you choose the distance 51,4cm between the two mics you will be able to record 180°. If your choir is even larger you can add a microfne at the left and on the right = Gross-AB (I don't know the word in English). Normally one uses omnidirectional microfones for this case but you should have not too much room-tone so cardiodid-microfones could be the better solution for you.
http://www.musik-produktion-createc.ch/Createc-Chor-gross-Aufnahme.jpg
Here is an Music-Example of this configuration (mp3)
Instead of that you can have all xm a microphone. There is a rule: The 2nd microphone should be 3 times farther away than the sound from the first mic....
http://www.musik-produktion-createc.ch/Createc-Chor-gross-Aufnahme_b.jpg
X/Y for each microfon position is not necessary. An ORTF over all can be give an even fuller sound but keep in mind that you will have more room and also time delays which should be compensated. More microfones are not always better. Nevertheless having more recources (channels) is always a good advice.
BTW Here is an example with EBS (over all microphones - mainly thought for the instruments, and 4 microphones for the choir). Keep in mind that these choir singers often are soloists. So the aim was here that you are able to here each voice... 😉
Best Beat