Is it permissible to pray in clothes that have been splattered with the droplets of water with which an impurity was washed, after a strong presumption that the impurity has been removed?

Wasswasa (obsessive whispering/doubts) is one of the most dangerous ailments, and its cure lies in ignoring it and not paying attention to it. Nothing is ruled impure except with absolute certainty. The default state of things is purity. As long as the matter does not go beyond doubt and wasswasa, then your prayer and your purification are valid.