I drove in ECO mode from Washington DC to North Carolina, I was getting close to 25 mpg. But on the way back, I drove in SPORT mode, getting around 16 mpg. I was flooring it a number of times too. Trying to stay at 79 mph whenever I could.
Normal mode, I read you only lose about 2-3 mpg off the ECO mode.
As someone that used to get an average of 8 mpg in TRACK mode on my 2017 Dodge Charger Scat Pack, I do not feel guilty at all leaving my ST in SPORT mode 'all the time'.