Studio One v5 supports a four decimal place accuracy when entered manually. It also flows between tempo points at upto four decimal places. So your tempo can read upto a maximum of 400 bpm, with an accuracy of upto 399.9999. Anything above that defaults to 400 BPM. So a tempo of 255.1234 BPM is a valid input when creating a song or tempo change point in the Tempo section.