Chanson de nuit is slow and a beautiful piece but it's on the grade 6 syllabus and i'd say one of the hardest in it - because the majority of it is all on the G string and there's soo much shifting. If i'm thinking of the same chanson de nuit as you that is

But it is a really, really nice piece
On the grade 5 syllabus i looove Tambourin by Gossec. Really happy upbeat piece and isn't too hard whilst still sounding impressive

Those 2 would be a good pair of contrasting pieces