The single pressure quoted in the manual covers all load conditions, if you run the vehicle empty all the time then you could lower it a bit but make sure the pressure is increased if you start hauling some weight around. Remember that a 110 weighs more than a 90 so you shouldn;'t use that as a comparrison (manual states that a 90 on 265/75's should be 35PSI on the rear, 40PSI with 7.50's fitted). LR spend a lot of time getting these figures correct and I have never had a problem with them yet.
If droping the pressure then make sure you do a check to see if the tyre is under-inflated otherwise you will start to get uneven wear (under-inflation results in increased wear on the outside of the tread, over-inflation causes increased wear on the middle of the tread). Also if you were to have a serious accident tyre pressures are one of the things checked and if they are found to be way out it could be claimed that contributed to the accident.
I always make sure the spare is over-inflated as that way it can be put straight on and the pressure dropped to match the axle onto which it is fitted, too low and unless you carry a pump you could be running uneven (it also allows for slight pressure loss while being stored).