If you drive on I-25 in Colorado, you better be going close to 80 in the left lane, otherwise you get passed on the right. The speed limit is 75 and you'll never get a ticket for going 80. If I cruise at 70, then my rpm drops from 2100 to 1840. That's no problem at all for my 430 hp LS3, since the cam is quite mild.

1120 rpm would only be 43 mph in my car, but it will cruise at that rpm in overdrive, unless you drop it into 3rd manually, or come to a hill that puts some load on the engine. Then it would kick down automatically. I tend to put my transmission in drive, not OD, if I'm just cruising around town, but bump to OD, if I'm cruising over 50 mph. I get over 20 mpg in the city. I've never had to opportunity to drive the car on a road trip to check the highway mileage, but it should be even better.