bromhead, I have been in the same analysis paralysis mode recently. The difference is that my 18" Comp wheels are already being manufactured, so there is no going back for me... I know that 265/60/18s will fit no problem in the spare wheel well, but the sidewall is what it is in that size - pretty good but not much better than sticking to factory 19s with a 255/55 A/T tire. 285/60/18 (and 265/65/18, which is virtually the same overall diameter) will fit as well with a bit of patience and "creative winching" when lifting the spare in the well - but only when partially / totally deflated and with the exhaust heat shield removed. I know this by experience on my 2006 Sport, which runs 285/60/18 Cooper Zeon LTZs and has pretty much the same clearances as the LR3/LR4. It'll also rub a tiny bit in places under full compression or steering lock, especially when new.
I am looking at splitting the difference, actually. 275/60/18 should still fit in the spare well under the car, hopefully fully inflated (so I don't lose TPMS on the spare tire, which is currently monitored since I ordered the HD package), no rubbing anywhere, and give me an extra 1/4" of sidewall and a wider stance compared to the 265/60 size. Trouble is, there is only one All-Terrain tire I can find in that size, the Yokohama Geolander A/T-S. It gets good reviews, a bit "mild" as an A/T, but realistically I will be on pavement 99% of the times, so a quiet and competent tire on wet/dry roads but still able to hold its own on most off-road terrains except deep mud (such as the Yokohamas) may actually be a good choice for my LR4 daily driver. I never see snow, so traction on snow/ice is not an issue for me.
I am also installing full Tactical Rovers armor underneath, rock sliders and fuel tank skid plate, as soon as my wheels arrive. Not going to extremes however - no steel bumpers and winches for me. Like you, I am concerned about weight of a car I still intend to use for work, family hauling and running errands every day.
