Richard, on my previous 110 and now my 90 I run the following on my BFG ATs:
Tar
Unladen, F/R: 2.3/2.5
Normal load, F/R: 2.5/2.7
Heavily loaded (with RTT, awning, jerrycan, 2nd spare wheel, loaded fridge, camping gear, etc): 2.5/3.0
Pressure must be set when cold, pref in the morning. I usually set the front first, then the back, and if need it, pump the back such that the 'bulge' on the tyre looks the same all around.
When leaving tar for gravel/dirt roads, measure current pressure and then halve. When returning to tar, measure current pressure and double.