Hi Alex, i just passed my grade 5 guitar with distinction, the pieces i picked where the following-
Telemann 'Gigue' from The Baroque Book
Sor 'Lesson in G' Op.31 no.5 from Sor Complete studies
Francis Kleynjans 'Simple Melodie' Op.79 No.11 from Modern Times Vol.3
'Simple Melodie' is a beatiful piece, well worth struggling with the counterpoint, 'Gigue' is a one liner so its very straight forward makes me wonder how it crept in the Grade 5 syllabus, 'Lesson in G' lovely piece typical of Sor's works.
Good luck with your exam!