I did assume that as the M3 with the longest advertised range the LR AWD would give me more range than the other options
Yes, that's true of course, but in practice the difference between, say, LR AWD and P- is small and a tiny variation to driving style will achieve that too (although that same frugal driving style applied to LR AWD would get you even a handful of miles more
).
I don't think that difference of, say, 20 miles ultimate range will make any difference to you day to day. if your journey is so tight that it would then Winter, Summer Thunderstorm, or battery degradation after 100K miles is going to, also, make that journey unachievable
That said, if you have 20 miles more range then there may be some days where it makes the difference between stopping to charge and not; also every time you do charge you need 20 miles less "top up". That is a worthwhile saving, if you have enough days a month when you drive out-of-range, but the chances that you have exactly the distance on a journey to avoid a charging stop is pretty long odds - based on my experience over nearly 100,000 miles.
20 miles more range may also make a difference if you have no home-charging and have to "go somewhere" to charge, once-in-a-while.
I find in practice that:
If my journey leg is range-challenged my driving style gets me there - but I will have planned (e.g. using ABRP) so that I know I can get there, or where I will Supercharge
If range is not an issue then I drive however I feel like
For me that is typically at least 20% more consumption than range-challeneged legs ... that "normal consumption" is also the case on a range-challenged day for a journey-leg which is within range of Supercharger - journey is shorter if you drive-faster and Supercharge-longer (up to about 90 MPH)
348 miles, I had remembered 350 miles. The current configurator for the P states 329 miles.
The range chart in this post
UK Model 3 order page open!
suggests that, at 70 MPH LR AWD and P- (both with 18" wheels and either with/without aero hubcaps etc) both have same range - and its nothing like 350 miles at 70+ I'm afraid, although at 60 MPH it looks more promising ...
(No idea if the data in that chart is accurate, but it looks like some trouble has been taken to get the figures)