Why do u want the .64 over the .82? U will eventually want a LSD diff.
Since u are going with a big V8. I would humbly suggest U go with a 3.46 and .82 OD (75MPH around 2750RPM). if U want a little more performance go with the 3.64 and stay with the .82 OD. (70MPH around 2750RPM).