I have an MSTC as well (from the first batch that Schoeps ever made), and frankly, I think that the ORTF arrangement that it provides will probably be the best-sounding way to use your MK 4 capsules most of the time. You might prefer the so-called "NOS" or "DIN" arrangements in some situations--but even if so, they're not all that different, so I think it's unlikely that you'll prefer them by enough to offset the advantages of the unitary microphone.
Coincident cardioids don't give very interesting results very often. With cardioids (or patterns with even lower directivity) some spacing between capsules is a "must" unless the sound sources themselves are in an unusually wide-spread configuration relative to your miking position. Otherwise the pickup in the two capsules will overlap so much that an inordinate amount of the direct sound will be reproduced near the center of the stereo soundstage. It usually takes a rather wide angle between the capsules (e.g. 120+ degrees) before there's enough channel separation for "real" stereo, and even then, it often feels as if something fun is missing, to me at least. (Technically this is because the correlation between the channels increases at lower frequencies, just where you want it to decrease.)
--best regards