The last piece I played the tempo is just over 60 BPM. What's the fastest tempo possible? I'd start from the fastest speed I can execute consecutive notes and work my way back starting from the shortest notes. Suppose the fastest notes I can play is at 200 BPM and a piece has 16th as the shortest notes. If I play at the top speed, 16th notes would be at 200, 8th would be 100, quarter would be at 50. A metronome set to 50 for each beat is the fastest I can go.
If a piece has 32nd notes as the shortest, my tempo would drop to 25 BPM for each beat to accommodate the fastest notes.
Obvious keeping your hands low on the keys and using efficient fingerings help. By the time we start tackling fast notes, the accuracy would probably go down significantly so always aware of the speed limit your hands can go.