For me, 3NT assumes points and entries in Partner's hand that he probably doesn't have - in order to access and cash those Spades, which you will need to make 9 tricks in NT.
If he does have those points and entries, then 4 Spades is probably laydown anyway.
But, if he doesn't, and I suspect he may not, I want to be in a suit contract.
So, if pass isn't an option, then I'm bidding 4 Spades.
D.