We ran a pretty good mk21/mk22 comparison this past weekend at the Phish show in Denver. Both sources were equal except for the capsules and pickup pattern.
The mk21's were run NOS, and the mk22's were run on the newer Schoeps STC 22 bar, (110 deg, 21cm). We tried to keep the levels on both the Sonosax and Mytek the same, they were definitely in the same ballpark. The mics were set up about 4 inches apart horizontally.
I've yet to listen to the mk22 source, so I can't offer my opinion yet but would be interested to hear what others think about the differences in these two capsules.
MK21:
http://bt.etree.org/details.php?id=548120MK22:
http://bt.etree.org/details.php?id=548155