FZ50 Replacement - Big speculative question

Well what are forums for anyway. From the very clever among you I ask:

With a starting point of 28mm wide, what long end zoom and apertures might one expect from a non extending lens of FZ50 dimensions based around:
A - a 2/3" sensor
B - a 1" sensor

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The FZ50: DSLR handling of a bright Leica 35-420mm lens that's this good: http://www.flickr.com/groups/panasonicfz50/pool/ (slideshow always good). And now add the LX2: http://www.flickr.com/groups/lx2/pool/
[Tomorrows camera is better and smaller than todays]