The gas station I fill up at recently switched over to E10. I thought I'd give it a try. What kind of a hit in FE should I expect?

Based solely on the difference in energy content between ethanol and gasoline, you might see a 3% difference with E10.

Actually 2.94% to be more exact .. given the data from your quote above ..

unless one modifies their driving style to make up the lack of energy given to them from the beggining

just modify your driving style to makeup that 3%

i got around 20 km a liter when i drove a civic 5 spd using advanced hypermiler techniques
and now I drive a salvage nwh20 prius that gets almost to 25 km/l with 195,000 km to date.