If you really want the Delta SkyMiles card, or any other card from Amex, this is what I personally would do in your situation. Try and apply for an Amex Zync charge card, cause its the easiest Amex to qualify for. This will also preserve all the history you already built with your Optima card, because the Zync should be backdated since 2001. This in itself will boost your credit score by raising your average account age, since Amex will report the history of your Zync back from the year that your Optima was opened, even though the account did not exist then. Use the Zync responsibly for at least 6 months, or a full year is even better if you are a patient person. Close out the Optima card-- it will not affect your credit score immediately, and the good history and age will still benefit your credit reports until the closed account is 7 or so years old and drops off (although some people have said Amex may still keep reporting it as in good standing because you will still have an account with them. Amex is weird). Then apply for the Delta card or any other Amex that you want, and if it was the recovery card that was holding you back before, you should get approved. Being that you are already an existing customer, Amex will only hard pull your credit report if you are approved, and they almost always pull Experian over TransUnion or Equifax. I recommend that you do not close out your Optima account until you have another Amex card opened, so you don't miss out on the backdating and resulting benefits to your FICO score.
Hope this helps