I personally recommend 5k miles on all of these vehicles, be it with synthetic or conventional. Not due to the oil breaking down, or not being able to properly lubricate, but to keep it clean. The less contaminants(the stuff that turns it black after time) the less build up you will get. This becomes more of an issue in the +05 vehicles that have over active PCV systems.

My recommendation for synthetic vs conventional is based solely on driving style, and conditions.

 

My understanding...

The oil doesn't break down...ever. It does get contaminated and worse, modern oil grade specs have gradually reduced certain "consumable" anti-wear additives (due to emissions requirements). You're likely to use up your additives before the oil gets dirty.

The benefit of synthetic is generally better "extreme" wear protection during high-stress operations (cold start, WOT, sudden rpm changes, etc). The base oil stock doesn't last longer than dino oil...they all last forever, unless perhaps exposed to extreme conditions which would destroy the engine anyway.

Given the cost of LR parts and service (and the apparent likely hood of the dealer screwing it up) I baby the thing. Premium gas and somewhat shorter than recommenced oil intervals.

Engines which specify premium usually mean it...it's not a power thing but an engine-damage thing. High-compression engines will knock sooner on low-octane fuel. Actually modern engines *should* have a knock sensor that will adjust the timing to eliminate knock but this will reduce power and you're obviously getting at least a little knock before the sensor dials it back. Any knock is bad, I've heard of engines which were susceptible to knock damage because the sensor system didn't respond very quickly.

There is a difference between Euro and US octane ratings, but you can tell which is which by the reading the manual or the label on the filler.

 

Well, I have done the 87 vs 91 octane (here in Canada) test, and can report, that my LR2 SE gets average 12.5 with 87 and 10.2 with 91. If I am just highway driving @ 100-110 (whicj it seems to like best) the 91 numbers improve to 9.3-9.8 . Not bad for a heavy inline 6 banger eh?

So in conclusion, any percieved savings in fuel costs, for me, are cancled out by better mileage.