A performance synthesizer is... a synthesizer. You play it, it makes noise, you perform on it. I did hundreds and hundreds of gigs using a 90s rompler and it was, and is, a performance instrument by definition as are pretty much all synthesizers.
The market is replete with synthesizers that have useful performance-related controls on them, though most people underuse them.
Are you talking about a syntheziser that, as you play it, allows you to drift off into happy circumstance-land? Modular will do that. Are you talking about a synthesizer that allows you to jump from one crazy way-out sound to another with ease? Hydrasynth will do that.
Arpangel wrote:I'm happy with my patches in Reaktor, so that could be a way forward, I just need the right controller, wide ranging, can be a conventional keyboard if required, have ribbon qualities and at the same time as that, play discreet notes.
Arturia do a half decent Easel emulation. It's probably not going to match your hardware experience but it'll work in much the same way and nobody listening will be able to tell the difference.
Don't get me wrong, I'm sympathetic to your cause, but echoing what Hugh said about the Buchla, if you need a something that looks like a duck, walks like a duck, swims like a duck and quacks like a duck you should probably buy a duck, regardless of your past record pertaining to duck ownership ;)