I just realized that the above comparison is not fully fair because the Oktava were fitted with their optional omnidirectional caps rather than their standard cardioid caps like for the NT 5, that are also modular but I have not got their omni caps. Here below some new recordings with the MK-012, omni and cardio, the Rode NT 5 and the Avenson STO-2. It's a kind of world tour since Oktava is Russian, Rode is Australian, and Avenson is American. The STO-2 are omnidirectional small diaphragm condensers (actually electrets), in a price range intermediate between the one of the Oktava and the Rode and the one of the Neumann KM 184.
I did not editing except for cutting the beginning and the end, applying a slight gain compensation for getting similar levels (- 3 dB on NT 5, + 1 dB on STO-2) and compressing in MP3.
I think that the differences are not so large (at least not in the proportion of the price, the ST0-2 being more than twice more expensive than the MK-O12 and the NT 5) and that the room acoustics and the microphone placement may have more importance that the microphones. Here the microphones are placed in a 20 cm A-B at 1,5 m height and 60 cm off the piano rig.
Don't take care to my playing: I am just starting to work on this nice piece from Schubert.
Edit : attachments removed because too badly played.