IMHO- as well stated above bike fit and comfort is really important .
Distilling these suggestions- have your EMS bike store order a CrossCheck frame,
build it up with great quality 36 spoke wheels, LX level components, a mtn bike
crankset with 28 & 40 chain rings, 11-34 cassette, Schwalbe marathon supreme tires,
get a nelson longflap or camper seat bag, lots of water bottle holders, a handlebar bag, make sure you can change a tire and be able to make minor mechanical adjustments to your bike. Once built up
commute to work with it as much as possible. Then go ride across the US, but don't race do take some time to enjoy the sights.
tire