Tommy is right on everything he wrote. Now, with that said, let me tell you why I went with a .64 OD with my 3.54 rear. That TKO 5th gear ratio gives me 34 miles per hour per 1000 RPM. I use 5th gear for nothing other than pleasant highway cruising and there is nothing I enjoy more than easing along at 2200 RPM, which is 75 MPH, out in the countryside, and the engine is at its quietest and is smooth as glass. You can actually hold a conversation with your passenger. That is the only thing my fifth gear is good for, but that's why I chose it. Now, it would also come in handy if I made a run to see what my top speed was, which I've never done. I think she'd top out somewhere in the 160's, but I don't know. But, that little item is on my bucket list... probably the last item, especially if the ol' girl blew a tire at that speed.
