I use the 617s regularly on a Jecklin Disc for piano recordings, but with the 1" Gefell MK102.1 capsules. I'll try to do a few things next month with the Josephson-branded MK221s, I haven't used them in a few years. Comparisons are hard, since the results vary with pianists and repertory, I find (and I only have two C617 bodies). I recently did a recording of a baroque string group with harpsichord with the Josephson C700S and it turned out spectacular (didn't even need the spots on the harpsichord); the same mic and position did not work so well yesterday for piano, clarinet and strings (Messiaen Quartet for the End of Time), okay when the music was soft but the reflections in the room (I think) muddied up the louder passages (and uncharacteristically noisy HVAC didn't help the quiet parts either). Maybe I need to get some of the Josephson cardioids with the petrified loufa screens (yes, I do like Josephson mics a lot).
Jeff