When I was in chorus and chamber chorus. We were recorded several times and it was always with a couple of mics suspended overhead and slightly in front of the group and it always came out sounding good. I don't imagine they were using really expensive mics, then again it was the 60s and perhaps what is seriously expensive now was not back then.
I agree with WST3, a stereo mic or two mics. I think some of the newer ZOOM stereo field mics might do a very nice job and you could mic two or three different ways. A stereo field mic. A couple on stands, and a couple suspended. then chose the setup you like best.
You probably need to consider the acoustics of the room too... especially when placing a stereo field mic. A couple suspended or on stands are going to be pretty much where they will be.
 
Good lick, sounds like fun!
J
 

Mics are here. They've spent the last couple of days on COLD UPS trucks, so they're just sitting in their boxes coming up to ambient. Testing starts tomorrow. First time recording with an M/S pair. I plan to use my mobile recording rig.
 
Help an aging engineer out here if I've missed anything obvious. My planned test sequence follows. If you don't give a crapola, and I expect most or all not too , you can stop reading now.
 
1. Using my PC, SONAR and Tascam i/f, test each mic (all 3 patterns, the -10 dB pad, and the HP filter).
 
2. Set them up as an M/S pair, connected to my Nexus 10 tablet, Audio Evolution Mobile for Android and PreSonus i/f (mic inputs 1-2) and record some audio at 48/24.
 
3. Export the Mid and Side stems to WAV files and copy to the PC.
 
4. Open SONAR and create a three-track project (Mid, Side, phase-inverted copy of Side) with appropriate routing to a stereo buss.
 
5. Make sure all of that works.
 
6. Set up the track and buss FX I want to start with, and save as a template.
 
7. Set up two MXL mics as a stereo pair (PreSonus mic inputs 3-4), and record some audio at 48/24.
 
8. Repeat steps 3-6, except for a stereo pair.
 
Once that's done, I can use either a pair of 990's or 991's (depending on which sound better in situ) for the stereo pair.
 
I'm finding the following table (from Shure) helpful:
 

Sounds like a good plan!
 
While you may become even more curious over time, that Shure chart is very helpful. I won't even mention patterns they left off<G>...

Ewph.  You have to be careful with those charts like the ones from Shure, especially when it comes to a spaced pair.  I know it is in every textbook and some big name studio guys do this because in the studio, a spaced pair, typically used for drum miking can be extremely wide, but this is not the use for orchestral or choir recording.  The AB or spaced omni pair should, in reality, be between 40 and 60cm.  It is the phase relationship between the two mics that creates the stereo image, not the proximity to the source.  Any wider than 3 feet, and you will have a massive "hole-in-the-middle" sound and increased phantom imaging (you won't know what direction the sources between the mics are coming from, sometimes they flip from left to right depending on the context), not to mention you will loose the phase relationship completely.  
 
I would take a look at DPA microphone's "microphone university" on their web site.  It lists the proper usage for an ensemble recording context.  
 
Regarding MS.  Most advocates for the technique in large scale ensemble recording will tell you the center mic should also be figure-8, not cardioid.  I whole-heartedly agree.  This will give you the same pickup pattern as a Blumlein pair, which is fantastic for choral recording because of the wide, realistic front image, and the equal ratio between direct and room sound.  You could also, and I prefer this, just use crossed figure 8's in a Blumlein pattern.