Summer is hot--sometimes ridiculously hot. In August I try to maintain altitude, which means mountain states, or stay right on the coast. There's little sense in trying to span from one coast to the other unless you like long stretches of straight highways contemplating unchanging horizons. And Texas, being hot with a tendency to thunderstorms and hurricanes, would be far off-course for anything I'd plan during August.

Unless I'm misunderstanding, you're looking for two-lane motorcycling roads (winding, smooth pavement, not insanely crowded), with points of interest at the roadside or within short walks. I'd start in Washington State, Colorado or California for ease of securing a bike as a non-resident. There's plenty of riding, plenty to see, and after 30 days you can trace your route on a map of the country and notice how little ground you've actually covered compared to what's available.

Two other obvious points: first, purchase and sales for a 30 day trip is fairly marginal. Second, a lot of the more popular attractions will be totally swamped, booked out, packed with slow-moving traffic; I'm thinking of Yellowstone, Yosemite, Glacier, Rainier, etc. This summer shows signs of being worse than ever in this respect. For me, that means I try to park and get away from the teeming hordes, usually on foot. That's not what you're describing.

Hope that's helpful. Note that there is much to consider, and therefore most of us will miss the point when trying to answer. You might have more success asking specific questions after you narrow things down for yourself.

Edit to add: I just noticed that you seem to think "everything" west of the Dakotas would fit into a 4-6000 mile trip. Oh my. I just took a 3500 mile road trip through Washington, Oregon, Nevada, Utah, Idaho in my van, hardly went anyplace at all considering what's out there, and returned home after 2.5 weeks frustrated by how little I'd seen and done....and I'm an old hand at this and didn't actually try to see many of the usual sights because I've basically seen them all multiple times. Maybe my taste is different from yours, but still.