Does dual motor increase real world highway range? or just overall EPA range rating?

I'm an early day 1 Model 3 reservation holder starting to consider the options I am willing to wait for. I will be using the 3 to commute 200+ miles 4 times a week, so my number one concern is to maximize highway range. 95% of my miles will be at 65-75mph Seeing recent speculation of 300+ miles on the larger pack is very promising to me, as I would prefer to not use range mode at all to reduce battery degradation.

Does dual motor increase effective range at highway speeds, or just in combination with city/highway driving? My understanding is the front motor is about 1/2 as powerful as the rear, and optimized for the city stop and go driving, and is idle at higher speeds. If this is so, it would make sense for me to save money and overall weight (not to mention time) and go for the single motor first run. On the other hand, if it is a 10% increase in highway range, I will definitely wait and spring for the dual motor. Does anyone have any insight or actual numbers on this? Thanks.