I just got back from a 525 mile round trip and I got 19.1 mpg on the way there and 18.9 mpg on the way back. As my previous best with the TH400 was 13 mpg I increased it by 6 mpg. A whopping 45% increase. As I live out in the middle of nowhere I am always driving at 55 mph or better. So I can really use the 30% overdrive. But if you just drive your car around town and seldom get it up to sustained 55 mph or better speeds a TH700R4 won't be any added benefit to you. In my case it was a great idea especially as I have the torque monster 454" ahead of it.