The AT3031 has a very flat response, reasonble sensitivity and a good price, but I don't see anyone selling matched stereo pairs. What gets matched in stereo pairs and how important is it?

If it's just sensitivity, does a slight mismatch in senstivity just move the center of the image, or does it degrade the image in some other way(s)?

I guess the easy answer would be; "it depends". I'm willing to bet that 99% of studios use matched stereo pairs, but I HIGHLY doubt... okay I'll bet my firstborn... that NOBODY can hear the difference in two mics of the same make and model... unless one of the mics is defective.

I did a stereo recording using an Oktava mk012 and a Rode NTK... (not exactly a matched stereo pair)... and it was surprising how good the stereo image was. If you match the actual signal strength between channels... no problem.

Okay so if you get another 3031 do you honestly think anybody can really hear the difference? I doubt it.

Generally speaking, Audio Technica's are very consistent. Unless you were doing critical music recording I think you would be fine with purchasing two AT3031's together. That would give you a greater chance of getting two mics that had been made together, shipped together and stored together. As much as I like 3031's, I doubt you'd be doing critical music recording with them, so in other words I think you'd be perfectly fine.
Of course even with a very good brand like Rode that ships stereo pairs that's not a guarantee. Back during the summer I received a defective pair of NT5's. Both mics had the same problem, but one was much worse. Unless these mics were damaged by heat in shipping, then they must have been defective in manufacturing. I received a replacement pair that was fine.
The 3031's and NT5's are pretty similar sonically, but I like the bass rolloff, pad switch, better clips, generally cheaper price (especially if just buying one) and smaller transport size of the AT's.
You'll find a much greater effect on the stereo image from how you place the mics in the venue as well as how you position the mics in relation to each other, than any slight difference in the mics from a consistent brand.
If in doubt, it's very easy to test and see if you can distinguish any difference in the mics.

I agree with Mr Gettemeier, some times two totally different mics even sound great. Spend the money you save buying good shock mounts and wind protection. The k-Tek KSSM (with the soft rubber) would be great.

My main venues are high school and community theater musicals, plays, and choral/instrumental concerts. Certanily not critical. I thought I'd bank on a stereo pair in front of the stage for events that aren't miked, and when the house is using mics and its board, I'd take a mono mix from the board and use one of the mics as a room mic.

Based on price and the discussions on performance I've read here, I'm deciding between Oktava MK012 and AT3031.

Any comments on my planned usage and those choices?

I've only worked with the Oktava for a little bit, it sounded quite nice. But I've got a lot of experience with the 3031. I like it's overall sound, it's not sticky on the top end like a lot of mics in that class are. I love it.

I like my Oktava (from the SoundRoom), especially with the hypercardioid capsule. When I compared my Oktava using the cardioid capsule to my 3031 in a theater, the Oktava sounded more open and detailed. However I judged this to be unsatisfactory because it made the poor acoustics of the space very apparent. The 3031 gave a more flattering recording.
I think that with the Oktava, you really would want to spend the extra money on getting a matched pair. That would push the cost well above getting two regular 3031's. It would depend on how much of a system you wanted to build whether the modular nature of the Oktava would be beneficial.

Thank you, everyone. The message seems to be that I can't go too far wrong with a pair of either Oktavas or AT3031s.