Greetings! Thaian207 I appreciate your desire for more range, but maybe before going to the expense of upgrading you can consider changing your driving pattern.
For example, here's a chart of SR vs LR Range vs Speed.
With and ICE car we don't consider too much that at higher speed our MPG drops since refueling is typically quick and stations are easy to find. With an EV driving strategy is a bit different, at least for me. For example, if I'm taking my M3 LR on a 200 mile day trip in each direction I'll have to recharge at some point since my battery pack limits my range to 325 miles (under ideal conditions). In reality, the range is likely less, which means I may actually prefer to recharge twice for shorter periods.
With the upgrade to 150KWH chargers at many Tesla SuperChargers charging speeds are faster regardless of your battery state of charge. You can even optimize the battery to accept faster charging by conditioning it on the way to the SuperCharger. So, on your trip tap the Icon to find the Supercharger on your route, and navigate to it. That will automatically start the battery preconditioning as you drive. When you get to the charger you'll charge faster, saving time.
As you can see from the above chart slowing down can significantly extend your range. On the SR M3 dropping to 60MPH from from 70MPH gives you about 40 extra miles of range. It may not matter for many of your trips, but if range is an issue you can drive slower and may be able to avoid having to charge en route. In fact, if you look at the chart you'll see that a LR M3 driving at 75MPH has the same projected range as a SR M3 driving at 60MPH! Speed is a killer for EVs.
There are lots of other strategies that may help as well. My point is that driving and EV is different from an ICE, and thinking differently about range and charging times can be useful to optimize your trip. Moreover, as SuperChargers increase in power, and software updates improve efficiency further, the need to longer range may not be as critical.
This chart shows how quickly the M3 (LR) can accept high charge rates:
As you can see when the battery is between 10-45% state of charge the M3 is very efficient at recharging. That could suggest that "topping off" with a high state of charge isn't an optimal strategy. Better to wait until your charge level is in the optimal range above. EG: If you charge at 10%, you can recharge to 45% at the highest speed possible. That may suggest that you consider two shorter stops instead of one longer one to maximize charging efficiency, and doing so quickly.
Again, my point is that EV driving is a "work in progress" with many things to consider. Perhaps it may be useful to hold onto your SR a while longer, play with some of these strategies (and many others available on the forum) and then decide if you really need to upgrade.
One final thought - it's rumored that in 2021 Tesla will have an entirely new battery pack with the potential to last for one million miles. If that's at all true, you may want to wait a while to make the best financial decision you can. I'd personally be a bit upset if I traded in a SR for LR M3 only to find out that if I waited the new battery pack is even more efficient and both charging times and range is improved.
Regardless, you can't really make a bad decision. Just decide what's best for you, and what your driving patterns are now and how they may change in the future.