Modern piece for DipABRSM

Hi. I'm learning pieces for my DipABRSM and so far I'm set on:
Schubert - Sonata in A major D. 664
Ravel - Sonatine
So i need a more recent piece (it says they want a "balanced" program). I'm allowed 6-8 mins of my own music, so I think i'll do that rather than play some of the modern stuff listed in the syllabus.
I've played Ives concord sonata movt. 3 (recording here: http://www.sendspace.com/file/kfxvzt ) and I really like that, but is it suitable to play just one movement?
My other thoughts are perhaps some Kapustin, but lots of it seem very difficult (how hard is the toccatina op.36?), what are some of the easier pieces? I have no idea as I haven't played any jazz-influences pieces before. Yedidia is great too, but I'm, not sure wich are the easier pieces...
Messiaen is listed (regards 2 and 4) but I think it's a little difficult, at least to memorize!
Any other suggestions? I love some roslavets too, but that also sounds impossible!
All the modern music I like is extremely difficult...