I take music GCSE, sitting my exam this summer. Absolutely kicking myself that I didn't take business instead of music. Business is a very easy subject; pretty much everyone in my school gets 8-9 in it. Music, on the other hand, our class average for a listening paper is UNDER 40/80!!! (At a grammar school too!!!) Just because you can play your instrument well, DOES NOT mean that you will do well in the GCSE!! I went in thinking it was a free grade 9... oh how wrong I was. 3 compositions and 2 performances later, I'm desperately hoping for a 7 in the GCSE, but most likely going to get a 6. Honestly my most stressful GCSE by far. Not even to mention the stress I went through for the coursework. On top of creating 3 of my own songs to an unreasonably tight deadline (which is EXTREMELY difficult as a piano player with no theory knowledge), I had to learn a whole DUET along with putting hours and hours of work into my ABRSM pieces to make sure they were perfect. As if that wasn't enough, I had to go and learn grade 5 ABRSM theory to even have a chance of getting a quarter of the marks. AND, on top of ALL OF THAT, we have to memorise every single aspect of 8 PIECES!!!!
My advice: AVOID MUSIC LIKE THE PLAGUE!!!