A correctly configured mailserver should reject your email (or mark it as spam) if you don't use both DKIM and SPF. It's safe to assume 99.999% of users use both.
Tell me you don't have professional experience in email without telling me you don't have professional experience in email.
Around between four and four and a half orders of magnitude for the Fortune 100, with five orders being the maximum possible wrongness.
A correctly configured mailserver should reject your email (or mark it as spam) if you don't use both DKIM and SPF. It's safe to assume 99.999% of users use both.