Like Alan, I was puzzled by the use of the subjunctive in some of your examples, particularly this one:
"Coge un par de plátanos, los que estén más maduros" - because to me it seemed that the speaker had indeed noticed that some of the bananas were riper than others. Maybe it makes sense, though, if s/he had not yet seen them - but in this latter case s/he would probably have said: "Coge un par de plátanos, preferentemente dos que estén más maduros" - [is that correct?]
I can understand the use of the subjunctive when it is referring to the future - e.g., your sentence-example which begins: Quienes lleguen… [because it is not yet known who will reach the top first].