Agreed, the .64 OD is often my recommendation for customers I do installs for, and my personal toys as well, as I like rear gearing in the 3.90- 4.50 range, the .64 OD responds well at highway cruising speeds and offers a comfortable RPM range for the engine, esp if outfitted with multiple carbs, and the MPG increase is often mind boggling, on cross country jaunts, HotRod Power Tours. etc I could muster up to 20-22 MPG cruising at 70-80 MPH with a 450 HP 440/6 pack and 4:10 gears, including a 472 HEMI running a TKO .64 OD and 4"10's could pull down 15-16 MPG on the events/runs, as long as you weren't tempted to put your foot into it