I drive my LR4 over 30K miles a year, most of them on highway. This car is a fantastic highway cruiser, as long as you can put up with the fuel bills, which will be substantial I'm afraid. The heft of the car in a relatively compact footprint makes it as stable as a freight train at high speeds, despite the brick-like aerodynamics you will always feel safe regardless of speed, even in fairly strong crosswinds. And you will absolutely love the command driving position to scan the road ahead for hazards, especially in heavy traffic. The seats are most comfortable to me (that's subjective), not too mushy and just supportive enough. Watch your speedo as it is very easy to reach illegal speeds in a hurry in this vehicle, thanks to the strong engine and quiet interior.
The longer wheelbase soaks up most potholes and road imperfections with minimal fuss and keeps the ride smooth and serene for you and up to 6 passengers, they'll all have enough room and never feel claustrophobic on long trips. And, the upgraded sound system in my MY2013 (Harman Kardon Logic 7 - don't know much about Meridian but the consensus seems to be that you should stay away from the base sound system and opt for the upgraded one if you are an audiophile) sounds excellent to my ear.
I can think of few vehicles I'd rather be in for highway cruising than the LR4. The fact the same car is so capable when you get to your off-road destination is all gravy, and what makes most Land Rovers so special and unique in the automotive world.