92% with 4 perfect cuts (messed up badly on the easy 12-sided shape). Don't know why, but it was a strangely fun exercise. "Brilliant" ad too (pun intended :D)
5 perfect gives you 100% on those 5 attempts but then your overall % is calculated based on at what margin you missed out on other attempts. ex: if you got 42% instead of 50% in an attempt then that would impact your overall %.