Just my humble opinion, but I wouldn't own the 0.64 overdrive. It drops the RPMs too far.
With your set up you will be very close to 2500 RPMs at 75 MPH. I can't see a reason to run a 0.64 unless you are trying to pass CAFE requirements. With a 0.64 you will be under 2000 RPMs at 75 mph and run the risk of blowing up your motor if you lug it while trying to pass someone.
Also, a 0.64 will be completely useless on the track. You might be surprised at how many people now track their cars. It is incredible fun. You might say you don't need 5th on the track...I would say, come and try Miller Motorsports track and red-line your motor in 4th (Oh, what a feeling), and then grin as you grab 5th and keep winding.
David
