checht, I just now noticed your reply #16 above, in which you asked two questions. The first one, I don't have much experience with, since I am generally the person paid (or volunteering, but in any case officially designated) to record a concert, so I generally get to negotiate my miking positions, and can make sure that they are either centered or symmetrically spaced. If I had to record from a single, off-center position, I don't know of any way to correct for the various problems which that would cause, and I would only do it for documentary purposes at best. (I can think of only one time I ever did that; the recording was never used.)
Your other question was:
> given that we're recording the sound where the mic is (a shotgun won't improve ratio of direct to reflected sound), why not use omnis, which I believe are the most uncolored pattern. I guess this choice would result in more nearby sound; what would be other downsides?
A directional microphone's pattern causes its sensitivity to vary based on the angle of arrival of each sound component. If the microphone is located where the predominant energy arriving on-axis (or nearly so) is direct, then its directional pattern will help bring out the direct sound.
But if it's farther back, where "on-axis or nearly so" no longer works as a proxy for "direct", then you'd have to compare its on- vs. off-axis frequency response to see what the mike will do to the arriving sound. If that frequency response is uniform (setting aside the relative attenuation that the pattern creates for off-axis sound), then all the sound components should blend together more or less smoothly. If the off-axis response is peaky or uneven, then as it becomes the main source of signals from that microphone, the more you will hear that uneven response acting as a filter on the sound. (Unfortunately most manufacturers don't publish the diffuse-field response of their microphones; you have to infer it from the polar diagrams--and many manufacturers don't even publish those except at 1 kHz, where they mostly all look good.)
In that respect, a good figure-8 is in principle the closest to ideal--except that it is bi-directional, so it really tests the assumption that "you are so far back that there's no point in preferring the front of the microphone" and in practice, there is usually at least _some_ advantage to favoring front-arriving sound; therefore a good supercardioid usually gives better results in practice. An omni isn't omni at high frequencies (I'm talking about microphones with studio-quality signal-to-noise ratios) so it favors the front a little, and/or dulls the sides and back, which is useful in most situations--but if you are in the audience area and have audience noise to deal with, then that's not a good choice, nor are "wide cardioids" or the like, unfortunately.
Finally, the very worst choice is shotgun microphones since their off-axis high-frequency response is so wildly uneven; variations of 12 to 15 dB within a single octave, and at angles of incidence just a few degrees apart from one another, are not unheard of. In addition, the diffuse field response of shotgun microphones integrated across all angles of arrival tends to be very dull--whereas with a good figure-8 or supercardioid this is not the case. Using shotgun microphones to record anything from a distance in a reverberant space is a basic misunderstanding of what such microphones are designed to do.
Now, like a stopped clock being right twice a day, good recordings can occur with any equipment if it is generally working and in the optimal place at the right time. But if you can only bring one setup to a concert, and you're looking to maximize your chances of getting a good recording rather than relying on a hit-or-miss approach, I think that good supercardioids give you the best odds overall. I used MK 41 for many years and have recently become fond of the MK 41 V.
Your MSTC is certainly nothing to sneeze at, though. Its MK 4 capsules are the small, single-diaphragm type, and have very good polar response across the frequency range. Again for recording in stereo with cardioid microphones, that type of capsule, with some spacing and a decent angle of separation (not 90 degrees, please!) is the best approach--while the worst use of cardioids for stereo in a reverberant sound field would be the large, coincident dual-diaphragm type at angles less than, say, 120 degrees which unfortunately is the great majority of stereo microphones in practice.
--best regards