I ordered my first Tesla so all this numbers are new to me. I make a similar trip between Pennsylvania and Florida several times a year. How those numbers translate to range? Since we retired we stopped driving non stop. We now take 4 hour shifts. Get gas and switch drivers. We also add an overnight that would leave us about 6 hours for the last day.
Roughly, the MS has about 100,000kw of capacity. An average of 350kw/mile translates into about 285 miles of range while and average of 285kw/mile translates into about 350 miles of range. Why the efficiency discrepancy? Well, the efficiency and range varies greatly based on the speed, temperature, incline, etc. just like it would in a gas car. The LR's 405 mile total range is based on optimistic ideal driving conditions...flat, moderate temps, normal speed limits. Any variation can cause drops (sometimes severe) in the estimated range.
For example, I'm on the road from Houston to Santa Fe (1000 miles) and back quite often in my current 2016 MS with a total of 267 miles of rated range. The best range is always on the return between Tucumcari NM and Amarillo, dropping in elevation, generally with a bit of a tailwind, in the spring or fall. In that case the 115 mile trip uses about 90 miles of my range at 85mph. The worst is the leg is in the opposite direction with a headwind, a few thousand feet climb, in chilly temps. In that case, the 115 mile trip uses about 200 miles of range at 80mph.
I know that's a long winded response, but the gist is that real world driving conditions affect the range considerably. That said, there are now so many superchargers out there that U.S. range anxiety shouldn't exist with a new MS and half a brain. After six years in my MS, I would never go back to an ICE. On my trips, I love to drive for a couple hours and watch the scenery change, stop to stretch my legs for 15-20 minutes while I'm adding a few electrons, then repeat. The quiet, smooth drive combined with basic autopilot makes the trip far more enjoyable and less tiring than in any of my previous vehicles.
Hope you get your car soon and feel the same way that I do. Cheers!