If I could also add, I have a '62 SS 409/380 that came with a BW T-10 and 3.70 posi rear. It might not be a fair comparison of automation transmission vs. manual, but those 3.70 gears, were way too much for me. It would kick ass from light to light, but highway driving, forget about it. I went to a 3.36 posi and have never been happier. Plenty of power. Lower rpm's when cruising. Engine runs cooler. All beneficial. I also forgot to mention that my '67 GTO came with a 2.56 posi and 4 speed. I don't know who put those in or why, but terrible. I changed them out to 3.55's. OMG. Thought I died and went to heaven. A great gear for that car and my driving habits. Of course, I couldn't leave things alone. I then went to 3.73's. Big, big mistake. I don't think performance was that much better and other things suffered. I gave this car to my son about 4 years ago and he beautifully restored it. He didn't like the gears either. Went to either a 3.31 or a 3.42 set. Much, much better. I guess what it comes down to is what you expect from your car and your individual driving habits. Best wishes with your selection, Nicholas.