I'm planning a 6 day road trip from Salt Lake City to Washington DC. I want to take some time to see interesting things (maybe venture off on some two-lane highways), but for the most part, I'll need to stick to the interstate because I need to be to DC by the end of the 6th day. I can't decide if I should take I-80 or I-70. Both take about the same amount of time, give or take a few hours. Any suggestions?