Basically it is all in how you take care of your vehicle, it doesn't matter if it is a land rover or any other make of vehicle. You have to remember that all vehicles have been tuned for a certain level of octane. The valves, timing, compression of the cylinders all play into how the engine is tuned. The ECU can change the timing to compansate for curtain fuels and they (LR or other companies) also set all of the above for different markets around the world. Will your vehicle run on less than 87 octane, the answer is yes, will it run at its best levels or get the best fuel economy, then the answer is no.
My wife Caravan has a rating of 87 octane, my Disco states 91 octane, my Buick states 89 octane. Will they run with the other levels, yes. How will they perform, that is all in how you drive, how well you take care of them and if you make any mods to the fuel, exhaust or air systems.
I am sure that this isn't the best explination, but I don't run less than Premuim in any vehicle I drive, but that is just me.... if fuel prices get to $3 or more, then I will look at either a more economical vehicle for a daily driver, or look into LPG or Diesel....
Just my thoughts for the morning.