Hi nomad248,
My suggestions are:
*2nd movement of Brahms' Clarinet Sonata No. 2 in E flat. This used to be on the grade 6 syllabus and is one of my most favourite pieces. You need to have a big sound for it but it's great and so is the piano part too - although you need a confident accompanist as it's very difficult. I think it's around 5 and a half minutes (dependant on tempo).
*2nd movement of Poulenc's Clarinet Sonata. I think this was grade 7 at one point and is around 5 minutes. You need to have good control for this and there is a slightly tricky run, but is achievable with practice.
I did both of the above for my A level recital. There's the 2nd movement of Mozart's Clarinet Concerto which is around 7 minutes so perhaps a little too long. The Romance from Finzi's Five Bagatelles is also nice and probably around 5 minutes (I played that as part of my diploma programme).
I'd recommend you have a look through the syllabuses to see what is set at those grade levels, and see if you can listen to recordings to get inspiration.
Good luck. Lucid