Bonanza V35 w IO520. Typical TAS is ~168, The planes range is about 750 nm. Our endurance is about 550-600nm.
Both Leslie and I have had mountain flying training (in the "hills" of North Carolina"), but we have traversed the Rockies 8 times; four round trips, twice in a 172 and twice in the Bonanza, including our flight from Daytona Beach Florida to Alaska.
Leslie is IFR rated, so she is the PIC. I have not had an FAA medical since 1975 so I am relegated to right seat. But I recently got a Cochlear Implant and my word recognition went from 5% to 85%, so I may just try to go for it again. But at 72, it doesn't make much sense.
OK! I'm just gonna play around with a plan from KDAB to KSUN, since that's about 1800nm. At that speed doing the trip in two days isn't unreasonable, could probably do it in about 6 hours per day over two days but I can definitely see how getting knocked around in the average Florida late summer day to start the trip might make you want to make the rest of the trip more relaxed.
First thing: Terrain. Even IFR, you can do this route in non-oxygen altitudes: SNY V6 OCS V4 MLD V21 PIH V500 MENIN.
Side note: I don't know why the FAA puts all these new T routes in and then doesn't connect them with intersecting Victor airways. T302 would be useful if there was a better way to get to MENIN for the approach, but you can't get from T302 to V500 except by going off airways which means higher altitudes.
Anyway, the route above makes it 1853nm. If we split it into three days of ~620nm each, you'd spend the first night just northwest of Memphis and the second night near Holyoke, CO. I'd suggest making the first day longer, though, and the last day shorter. You'll be freshest on day 1, and the flying will be most challenging and fatiguing on day 3. And what do you know, Gaston's (3M0) is right on your route, about 722nm into the trip. If you're comfortable flying there (3200' grass, in the valley, LOTS of PoAers have gone before. The best part about this is not having to schlep everything from a plane to a car to a hotel, and dinner is right there in the restaurant on site.
For the first day, then, I'd go to 04M, about a 3-hour leg, for some cheap fuel ($4.56/gal) and a quick break (eat a lunch you bring from home either on that leg or at the stop), then continue another 1.5 hours to Gaston's 3M0, eat, relax, overnight. No need to buy fuel at Gaston's, and you'll be a little lighter for departure without it.
Day two, breakfast at Gaston's, and a 2.5 hour leg to Lexington, NE. Fuel ($4.99/gal) and take the courtesy car somewhere for lunch. In the afternoon, you'll have an easy sub-1.5 hour hop to Cheyenne to stay overnight. KLXN SNY V138 CYS KCYS.
Day three, might as well top off with fuel at KCYS - it's not gonna be cheap from here on out. 1.5 hours via MOIST V6 OCS KRKS Rock Springs, stop and grab a courtesy car for lunch if you need to, or just take a break, or don't bother stopping and press on for the last 1.5 hours via V4 MLD V21 PIH V500 MENIN KSUN... Or if it's VMC, take shortcuts as appropriate. Should be some good views on this last day.
With 11 total flight hours, a 2-day trip shouldn't be too hard either.