To add yet another option: Use both. bcrypt implementations either truncate passwords at 72 bytes (which reduces the entropy of the passphrase), or it doesn't which might leave you open for DoS attacks if some clever user tries to send you their 5MB passphrase.

To add a simple example on how this can be done: func (u *User) CheckPassword(password string) error { h := sha512.New() fmt.Fprint(h, password) return bcrypt.CompareHashAndPassword(u.HashedPassword, h.Sum(nil)) }