While US 50 being trunk is a little more justifiable, granted that its much busier these days than its reign as the "Loneliest Road in America", and links some regionally significant places like Fallon, Ely, and Delta, UT (with even more major highways and cities located west/east of this stretch), I would probably leave US 6 at primary, since it sees even much less traffic than 50 and connects even less population centers and major highways directly. It is a cross country route, but is very rarely used for such. In fact, it is notoriously a relatively pointless US highway for much of its route (aside from places like New England or between I 15 and I 70 in Utah) given that most of the parts that do directly connect major population centers have been successfully bypassed by Interstates, and segments that aren't bypassed usually only link smaller communities and are very lightly traveled, such as the case with it in Nevada. For example, US 6 barely sees about 200-300 vehicles along a stretch like the route between Tonopah and Route 318 because of its isolation and connections only with Ely and Tonopah, the latter of which is an even smaller community.