You didn’t say where in your back the herniated disc is, but I’ll assume it’s your lower back. I’ve had two lower back surgeries for herniated discs myself. At any rate…like a couple others have indicated…I think your primary consideration should be comfort (position) WRT your back injury. I mean you’re riding a road bike. Unless you’re riding on roads comparable to Paris-Roubaix, there shouldn’t be so much impact on your back. And, you’re posting in the 50+ forum. I know we’re all always concerned with speed. But what records are you trying to break? What race are you trying to win? I say longevity is the primary concern, and do what ever you have to do to keep riding comfortably.
Dan