The world traveling vehicle of preference would be the Defender. That being out of the question for those in the US. The LR3 / LR4 is a great choice. There is not anywhere I can think of in the US you could not get premium gas. In a pinch it would run on regular, but it would mess with the advanced computer systems in the long run. The LR4 being the "perfected" version, has some improvements, such as relocated electronics, and such. The LR4 has a bigger engine, which is a real plus. The LR3 is every bit as capable, as most systems are common to both vehicles. If anything the LR4 is probably has more gadgetry which seems like it could potentially leave more opportunity for faults.
All in all if money is no issue, why not spring for the 4, and the extended 100k warranty. Either way, you won't regret it.
All that being said, there are a few things I would want on a new one if I ordered it.
1. Locking rear diff
2. Heated Seats (wish they had A/C)
3. Nav - absolute must
4. I hear they have an 8 speed coming? Not sure--
5. Rear video system would not be a deal breaker, but nice if you have kids.
6. Do not buy LR accessories such as brush bar, winch, roof rack... You can get better grade stuff from Lucky8 such as Baja Rack, Rover Specialties Rock Sliders with rails (steps) And so on.