From what I understand after 96 you can take it out without ill effects. 95 and earlier you will toast the 249. Taking the DS out won't do anything for your mileage. You're still turning the entire driveline, the only thing missing is the turning of the front shaft. You don't have lockouts so your front end is still all spinning an dragging just the same if you were pushing it with the DS.
I'm now at 4.10 and 285s. I get 14 in town and 16 on the highway.