The over drives and the multiple gears are what will keep a V8 and higher powered engines more viable longer. Hell anyone can sell a good old 4 speed today and most people would have no issue with it.
The fact is that the extra gears are what deliver the MPG in the more powerful engines by letting them run bigger gears and still letting them lumber down the road for the higher EPA and Emission numbers.
If there were no EPA numbers to meet and CAFE mandates by the government we all would just be fine with a 5 speed with on over drive gear.
Today you may want to note with most cars you drive they all lumber around 1600-1800 RPM down the highway. This is why GM puts in sound canceling in the Nox and a few there cars as the Ecotec has a drone at that RPM. It is a matter of meeting the RPM you need and then tailoring the gear box and car to meet it to get your numbers.
I have put enough skip shift removers in Corvettes so we do not have to deal with that. And most performance car I drive today I only see 5th and higher on the freeway.
