Which 35mm rangefinder lens for nex 7?

As far as RF lenses on the 7 esp, but even on the 5n, it's hard to trust anyone but yourself.

Many are ready to opine one way or the other, few have samples, and the variation in individual pickyness + the hyper-sensitivity to focus of the 7 = many unreliable reports.

The 7 is becoming famous especially for wide aperture issues, even on E and alpha lenses---but not all. This is in addtion to the colorshifting with many wides.

If fact it can deliver great images, but everything needs to be right.

If your only issue is cornerfix you are about to waste far more time lens hunting than you would cornerfixing.

Better even to sell the 7 while it is worth something and get a 5n or GXR, both which will like your summicron much better.