Now that you can play 8ths at 250, you can also play 16ths at 125. 120 is a very common tempo in music. You should drop your metronome setting by half and practice sweeping 4 notes per click. This will be a bit harder at first (less clicks are harder to subdivide the beats in your head). Now, put on a song you know around 120 tempo (just start a song and line up the metronome with it, if it's about 120, good, otherwise find a different song). Say that the chord progression is something like G, Em, C, D. Try sweeping these chords with 16th notes over the song. This will give you not just sweeping practice, but practice playing in time with other musicians and feeling the pulse of the drums rather than a metronome.