Well, look at this route:
North to I-40 West, 93 N into Las Vegas, 15N through NV & UT, 84W into OR.
There are a couple alternates with fewer gas & food & lodging stops, but that sounds like what you're after.
Probably 3 days, 2 if they get after it.
One can maintain high speed on NV 95 but it's desolate.
Any 2-lane in ID (95 or 93) is pretty slow average speed.
I've driven all those roads, never a worry.