Alot of my road (4wd) cars I use for online racing (usally 530pp sports soft / 585pp racing hards) have either a 90/10 - 80/20 or similiar split.
Most of my diffs are setup as:
20 - 10
24 - 12
40 -10
(stock would be)
10 -10
40 - 40
20 - 20
Basically, have the outside front wheel spin and the inside rear wheel spin a TINY amount. There's so many combinations of tyres. power gearing etc etc it's impossible to be 100% accurate in actual figures, until I know what car, power, tyres etc etc.
But thie general priniciple works well, the car semi 'drifts' out of some corners, constantly turning in - so no understeer.
It also helps as 4wds tend to murder they're front tyres, so camber / toe etc is usually a little less than average.
Loosen the rear end as much as possible, whilst still retaining stability / grip, this will help the front turn naturally and again help front tyre wear.