I haven't done a long term stint with the Fit, but I've driven the sedan variant out here in Asia (I'm on the Fit waiting list, though).
You're correct... manual mode gives you a shorter top gear, so it's not really worth using except when you want to overtake.
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In my experience, at a steady 50 mph on level ground, well over 50 mpg is possible.
At 60 mph, over 40 mpg is possible.
In traffic, it's better than the old Fit, but not as good as the Mirage. Still... it's a very impressive drivetrain.
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The new CVT, with its torque converter, is supposed to be more durable than the dry-clutch CVTs Honda has used in the past, but they don't take kindly to being beaten on, and they can get pretty "slushy" in sustained hard driving. Probably not good for the life of the box. Best to take it easy... but if you're an EcoModder, you're probably going to do that, anyway.