If you buy a new iPad with a retina display, you will download 1080P movies over wi-fi, not LTE. The problem is the price plans that are available from AT&T and Verizon.
Netflix estimates that an HD movie will take 'up to' 2.3 GB per hour. This means that one hour at 1080p can use up your entire 2GB to 3GB of data that you get on the carriers $30 plan. The solution to this is to download your movies over wi-fi before you hit the road. On the road, you will just do basic web browsing and email so you don't eat into your cap.
So, the question is ... why do you need LTE if you can only use it use for 3g-speed data downloads? Or, why do you need the retina display over LTE if your browsing caps limit the quality of the content you can see?