I could have sworn I posted a reply to this topic............ anyway!
I did Danse Rustique when looking at grade 6 and I think it's definately a good one - it has contrasting sections and used a variety of techniques. It was at about this level (grd 6) that I began to feel the pieces on the syllabus were something to get your teeth into - lengthy, varied and technically challenging - hoorah!
I also looked at Siciliene & Air de Diable (if that's the one you mean!) and found the sicilienne great, it's quite easy to get it flowing and with relatively few position changes. In the Air there were a few technical passages I struggled with but hey, can't have it all eh! The tenor clef is managable aswell

Actually I played the sicilienne for my marines audition, it went well
At the moment I'm working on a great piece called Appasionata by Saint Saens (amongst other things) and I love it - it also has contrasting sections and a variety of techniques, what's more it's exciting and dramatic! Maybe you could look at this one sometime?
Another good one is Tarantella, I can't remember if it's grade 6 or 7 though......
Alice