From what I've heard it's supposed to be hard and JC too. So my question for u if it's ur passion y didn't u pick it for Junior Cert??! If it's a recently found passion and U really are passionate for it then I suppose go for it :)
I am extremely passionate about music. I have grade 7 in classical flute, grade 3 in jazz flute. I used to live and breathe music, there was nothing I would rather do with my time than play my flute.
Due to picking music as a subject I began to despise music. I gave up music and stopped playing music for almost 2 years.. Honestly it absolutely wrecked what I had as a musician - passion.
Maybe that's just to do with my school or my teacher/class but if there's another subject that you're debating on and you're not planning on doing music in college then I wouldn't pick it.
I believed in making music not learning formula after formula off by heart as my teacher taught us to do. So for me it was the biggest mistake of my music career.
If you're asking if you'd be able, having grade 4 you'd definitely be able for the course but you are at a slight disadvantage when it comes to aspects like melody writing and the chord questions.
Hey that's just my opinion it's really up to you. Sorry for making this so long but best of luck!