As for total electrics aka the Tesla's of the world, they're not viable until you can charge them fully in the amount of time it would take to pump 15-19 gallons of fuel. Right now I can drive six hours from my place to my folks with a 20 minute stop to stretch and answer mother nature's call. Last I saw in the Tesla literature, that same drive would require 3 to 4 30 minute stops to complete. At 4 stops, that 6 hour trip just became 8 ours.
Don't understand your math here... at 75 MPH for 5.66 hours is 425 miles. Tesla 70D has about 236 mile range at 70MPH. So maybe you have to stop once or maybe twice for 30 minutes or so to super charge. I don't think it would be 3-4 times. Of course, I'm also assuming you could charge at your destination somehow for the trip back. You could also drive a little slow (60mph) and gain another 40mi range each charge. I guess there are a lot of variables here, but I think in general it's not as bad as it sounds.