How difficult is it to "crack" or brute force the NGRAVE "Perfect Key"?

The purpose of a brute force attack would be to find a private key that would generate the same Public Key as used by your wallet. We call this a 'collision attack'. The key generated by ZERO has a length of 256-bit, which equates to 128-bit entropy. This key length has been accepted as the de facto standard in the crypto community.

We can cite the Bitcoin Wiki: "it is more likely that the Earth is destroyed in the next 5 seconds, than that a collision occurs in the next millennium."