Dont forget that the Diploma is a recital, lasting on average 30 minutes. Grade 8 exams last at most 30 minutes for the whole thing (including scales, aural and sight reading). The FRSM is 50 minutes recital.
This level of staminia has to be built up by years of practice and experience.
On top of the recital (playing the notes and 'performing' the music) you also have to construct the programme, write programme notes (or essay), sit a Viva and perform a Quick study.
In the Viva the examiners will chat to you about your instrument, the music you have chosen, wider issues based on your programme notes, and deeper questions on music/instrument/composer history. This is your chance to show that you have a deep understanding and knowledge on 1)your instrument 2) the repertoire available for your instrument 3) the key historic elements of your instrument (composers, compositional devices etc) 4) General music history. You will need to call on all othese to construct a persuasive case to back your answers. You can not get away with just learning the pieces as one does for Grade 8. You have to actually have a lot of musical knowledge which you can call on to understand what is behind the dots on the page. The higher the level the more indepth the questions.
Then there is the Quick Study. As I have been told by others here, it is NOT sight reading. You are given a Grade 6, 7 or 8 standard piece and have to perform it to the standard you would if you were sitting a grade 6/7/8 exam (but you only get 5 minutes study time, and no accomapaniment). The FRSM piece lasts 10 minutes with only 5 minutes preparation time!
http://www.abrsm.org/resources/performanceComplete.pdf see page 14 for Fellowship exams.
This exam is designed to test your performance, knowledge and ability- and prove that you are worthy of being a Fellow of the Royal Schools of music (in other words the same level as the lecturers!!)
Some of the pieces may 'seem' easier, but can you play them as well when you have been performing for 25-50 minutes and your concentration is lapsing? Also can you explain why the piece shows that it is by a certain composer and why it is important to your instruments historical developement? (and this gets a lot harder as you go up the exams!) Can you automatically use the correction technical language to describe details? See
http://www.abrsm.org/resources/performanceComplete.pdf for examples of the submissions.
Also dont forget the the exam will be marked at a higher level. All details must be observed and mistakes will be marked harshly. Even if all the notes are correct, you must still observe all the performance directions perfectly and consistently throughout the recital- including true historical performance directions.
DipABRSM = End of Year one in a music degree
LRSM = End of Music degree level
FRSM = End of Masters degree.
In other words, could you write a postgraduate level dissertation in your programme notes and discuss with the examiners off the top of your head the intricate detail of every composers life, the instrument and all wider music?
Here is a link to the notes for candidate submission
http://www.abrsm.org/resources/writingProgNotesApr05.pdfIf you have done a postgraduate degree then you will probably have the research skills required, but unless you have years of musical knowledge and experience then it is better to work towards the diploma first.
Also if you are under 16 then the ABRSM do not allow you to enter for the exam.
I hope that helps- it is a very expensive exam to enter so make sure you think carefully before you commit to doing it and sign up for extra tuition etc! Good luck!