You're getting a lot of advice here based on supposed desirable qualities that are highly subjective at best, and "magical" at worst. (This seems to be typical of the loyalty people feel to Leica lenses.)
Your only hope is to figure out which of these alleged qualities are important to you in your Summicron shots, and then compare on that basis.
Objective data will be of no help here: The Nokton is an excellent lens, delivering high edge-to-edge sharpness, good contrast, and smooth rendition of out-of-focus areas, but only you can determine whether or not it will have the "magical" qualities you like.
A sensible strategy, if you can afford it, might be to hang onto your Summicron until after you've bought the Nokton, so you can compare the results, and then sell the Summicron separately rather than trading it in. You often get a better financial return this way anyway.