I bet a rough estimate of 275-325 will be what people like me are targeting. I don't need it to be exactly 300.A 70 kWh might not get the magic 300 miles range... that would be a mistake.
There are a few reasons why:
1. It anticipates some battery degradation over time and above and beyond the warranty.
2. I live in the midwest where weather can deteriorate sharply (freezing) and require more heating power.
3. I, like a growing share of Tesla buyers, won't have access to nightly charging so I need the 80% charge to meet my usual driving needs with a once-weekly charge. 300 miles of stated range gives me access to 160-240 miles of routine driving depending on the time of year. (below freezing weather in the midwest will increase power needs)
4. It makes highway driving much easier allowing me to get faster charging rates, make fewer stops along my route, and enjoy greater travel freedom generally.
If I only had a 235 mile range to begin with, then I would be stuck with 188 miles of range at an 80% charge level. The same level with a 300 capacity provide 240 miles of range. That 50 mile difference makes a big difference to someone like me who wants to charge once a week during a normal week.