I'm shooting a school concert tomorrow, I have two Cardioid mic's which I spaced about 50" apart in a test run. I usually choose the best source for a given script of dialog then convert it to a mono feed however I feed like playing with stereo for this shoot. Is an AB (spaced) stereo technique advisable for a school concert? The actors are relatively centered on stage during dialog. Thanks in advance.

With cardioid mic, best setting is ORTF. 17cm apart, and 110 degree.
Or, try NOS, 30 cm apart, and 90 degree.

50" is way too far.

AB recording usually use OMNI mics.

I'm shooting a school concert tomorrow, I have two Cardioid mic's which I spaced about 50" apart in a test run. I usually choose the best source for a given script of dialog then convert it to a mono feed however I feed like playing with stereo for this shoot. Is an AB (spaced) stereo technique advisable for a school concert? The actors are relatively centered on stage during dialog. Thanks in advance.

It needs to be mono compatible however as not everyone viewing the video will have a stereo setup. I'll agee with Anthony, 50" is not a good idea. Too far for ORTF or near-incident techniques and too close for A/B. In order to avoid phase problems, the mics need to be spaced apart by at least 3 times the distance of either mic to the sound source.

Here's a good summary of several common techniques
http://www.schoeps.de/PDFs/stereo-recording-techniques-e.pdf

Thanks guys you saved my production, I went with my first XY setup. Stereo rules! :)