Thanks Philippe,
It's interesting the Summilux ASPH and the Summaron 2.8 are holding the same values at the extremes. The higher contrast Summilux is not clipping either end and the Summaron isn't flatter with less tone in the deepest shadow.
The big difference that sets the Summaron 2.8 apart is it puts more tone into the middle quarter tones and it's a very visible amount. It's got a fatter curve. So you won't really be able to 'get an extra stop' from a high contrast scene because of lower contrast in the Summaron 2.8 as it's recording the same values at the extremes as the current ASPH.
35mm-compare.jpg
These are from you f/5.6 shots:
summaron35-2.8x.jpgsummilux35x.jpg