Look at it this way, you are paying $10k for 30 miles of added range for the 85D. Is that worth it to you? Are you driving so far that an extra 30 miles will mean the difference between finding a charger or getting stranded? I'll bet most people can get by with a 70D and a little bit of planning.
You're getting a lot more than just additional miles with the bigger battery - additional performance and SC charging speed also. If you can, I would opt for the 90D over the 70D.