How difficult is piano sonata no 17 - "The Tempest"? Just wondering where it lies in terms of difficulty? I'm roughly a grade 6 standard (RIAM... I don't know the British/American equivalent) 

I've yet to sit the grade 6 exam which is in October, but I've already finished my set pieces so I was looking for another piece to keep me occupied. What do ye reccomend? Give it a go now, or wait another year or two before attempting.

I've been playing 18 months for context.