Quicksilver's powers were enhanced by Isotope E during his ongoing series. This permanently increased his speed from 175 mph to supersonic velocity.
Pietro lost his speed to the Decimation, but gained new temporal powers in Son of M #2, and bonded with the Terrigen in #6. These abilities were lost in X-Factor (3rd series) #19, but he regained his speed in X-Factor: The Quick and the Dead #1. Following Uncanny Avengers (2nd series) #1-5, it was revealed his abilities were derived from genetic engineering by the High Evolutionary, and were not mutant in nature.