This is a very good question. Other than more redeemable miles, the additional benefits would be insignificant to me. So if your desire is to get higher status so you earn at a faster rate, I'd recommend credit cards. Sounds like you have a decent spend rate, so if you get the Amex Reserve, Amex Plat, and Amex Business Plat, you can earn 70K MQMs without setting a foot on a plane. You have to spend 160K on your cards to hit those thresholds, but if you are using them for things such as paying estimated taxes, booking $60K in plane tickets, daily spend, etc., that may not be an issue for you. FWIW, you would also get somewhere between 230,000 and 390,000 redeemable points for that spend on the cards. The difference is whether you earned 2 pts/$ or 1/$.

Also, assuming you have a business, I'd recommend signing up for the Sky Bonus program. Points on expensive business/first tickets from a non-hub really add up in that program.

One other thought is the Delta Jet Card Program. You'd have to look into the details, but my understanding is that you can use the card for commercial flights and also get a discount on certain (Full fare?) tickets. At the $100K level, which is good for 2 years, you also get Diamond Status.