Overdrive or don't worry about it? !

I would say OD based on OP comment of bad back and not wanting to do the work at changing the center section. Really takes less than an hour. I am running 3.91 typically. Just picked up a cheap ($150) 2.94 open 489 rear end (bbody) threw a spool ($90 from Dr Diff or Quick Performance) in it for the drive up to Mopars in the Park. 5 hours each way. 2500 at 70mph. Was at 3000 at 60mph. Totally a different car on freeway now.