If you've played FI, you already had a taste of the Moonlight 3rd movement, at least one bar of it anyway.

After you sightread through Moonlight you may discover a little familiar surprise.
The Moonlight uses different patterns than FI (mostly). Extended passages of broken chords, Alberti bass, tremolos. If you can manage the tempo of FI, the Moonlight 3rd is likely to be within your reach.