I have had a love/hate relationship with the Mark VI soprano forever. I buy one - love the sound but hate the palm keys and sharp low C. Sell it - then I miss the speed and lightness and buy another. Back and forth going though 4 Mark VI soprano. I've even added Front F's to two of them. Alas - they we just too expensive to keep and now they seem to be selling (at least listing) for $4K.
I have a modern soprano that seems to work and put the whole matter to rest. Recently I was talking to a local pro and he's playing a Vito/Yani soprano from the 70's. Basically a S-6 Yanagisawa which is a Mark VI copy. Found one on E-bay for $900 including shipping.
Came in today and it really feels like a VI. Maybe a bit lacking in the tone department but the speed, lightness, clearity of the VI is all there at a quarter of the cost. Don't know how long I'm going to keep it BUT since it doesn't cost a ton there's no hurry.
If you're looking for a VI but $4K is out of the picture - try one of these Vito/Yani sopranos. Very cool under-rated soprano is a world of over-the-top expensive sopranos.