Assuming your talking about driving performance only, that is not necessarily true. The bigger battery will enable better driving performance only if the power output from the battery is the limiting factor. Using the Model S for example, that is the case for dual motor vehicle, where you see jumps in performance for various battery configurations on the dual motor car. However, if you look at 0-60 times for the S60, S70, and S85, they generally hover around 5.4 - 5.5 sec, right? In this case, I presume its mostly the single large rear motor that is the limiting factor, and a larger battery won't change that. (Now, larger battery will improve charging performance, which I also find valuable.) To relate back to your BMW analogy, I expect the larger battery plus dual motor to be about a $10K upgrade total (ex. $6.5K for battery and $3.5K for AWD). That probably gets the Model 3 0-60s into the mid-upper 4 second range.