Overdrive or don't worry about it? !

I really don't see you as a 1/4 mile racer (or at least on this site). Here is something to consider. Your 390 will have a ton more bottom end torque than what you have now. Perhaps you could drop down to 2.94's and still be plenty happy with bottom end and you'd cruise 70 mph without a problem. Just a thought. OD is a great way to go....