please Help on the pieces?!

[10leungchuny]

Hi, my name is Anthony I am new to this forum so nice to meet you guys. I know it's a bit rude to just have a first time post as a question... if I by any chance have offended anyone, I am really sorry.
I'll be doing my audition for music college (possible Leeds College of Music) around next academic year for composition study although they ask for a 10 minutes recording around grade 7-8 along side a composition portfolio (the portfolio part is complete but waiting to record).
So I am kind of panicking on what i should be performing since i am still at Grade 5 as my piano teacher loves all his students to get distinction in exam, so yeah... :/
But I manage to picked some out of what i want:
Rachmaninov- "Six moments musicaux no.5"
Mozart- "Piano Sonata for four hands in D major 1st movement" (already learnt the secondo for my ensemble this year but don't know what difficulties its clearly at)
As I've mentioned before I would like to know what standard grade for the Mozart's Four hands D major will be at, and want to know is there any good advise for learning Rachmaninov Six moments musical no.5 or any hard piece effectively

Thank you for reading
Anthony