When putting more than a 4" lift kit in a Patrol, you will be faced with a very significantly higher cost than for a lift lower than 4".
As I see it, this is the kind of "additional" work you are looking at when lifting includes:
Up to 2": Lower rear gearbox mount, caster correction bushes, Anti roll bar extensions.
2" - 4": Above plus longer brake pipes, compensator extension and diff breather extensions.
more than 4": all of above, plus adjustable or extended panhard rods (front and rear), drop boxes or special front leading arms (camber correction bushes are not enough) and possibly adjustable rear upper or lower trailing arms and also extended bump stops.
Therefore, I beleive the cost of a properly done 6" lift is at least double the cost of a 4" lift, and propshaftswill be put under additional strain and therefore last less well.
As Sias has said, ground clearance remains unchanged (except for the effect of the larger tires), but the LWB Patrol's weakest point in terms of off-road clearances and angles is the breakover angle, due to our extremely long wheelbase, and this will be improved by the lift.
Any lift will compromise on-road handling, and therefore your ability to avoid an accident. On a 2"-3" lift the effect is probably negligable, and if you have fitted one of the better kits on dirt roads you may actually be better off purely because of the quality of the shock absorbers, but I would think that by the time you get to a 6" lift you would definately have to reduce your cruising speed. In an accident a lifted car would probably roll that little bit more easily, but other than that I doubt it will have much of a predictable effect, as it will depend on exactly what you hit.
IMO, stay away from body lifts and spacer lifts.
Body lifts are only cosmetic and do not improve off-road ability at all.
Spacer kits improve approach, departure and break-over, but usually reduce travel and may be bad for the car unless the bump stops are similarly spaced.
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