I’d like to submit a strategy:
Rank designs based on the percentage of G and C bases that are part of GC pairs as a fraction of total G and C pairs.
That is: score = (200 * number of GC pairs) / (total G bases + total C bases)
So a design where all Gs and Cs are part of GC pairs would score 100, and a design where all Gs and Cs were either unpaired or part of GU pairs would score 0.
If possible, I’d like to exclude from the calculation G and C bases that are locked, such as in aptamer rings that are fixed for a given lab.