That is the current set up I have on my rig. It was what the rig I chose came with - so I did not specifically request the 20", getting the HD package was my main driver.
I have been doing a lot of off roading (almost every weekend since I got "Henry" at the end of January 2011). Probably the highest rated trail I've done was around a 3 out of 5.
the tires are at 38/42 - if I decided to air down, around 33/34 seems to be a good point. But generally I don't bother to air down.
W/the 20" rims - you have to be more careful about rocks, bumps etc that you would if you had a tire that had more 'airdown' abilities. Yes, you will ding up your rims - but then again, I've seen LR3s w/18" that also have dinged up rims too.
I've been lucky that I don't take my rig out w/out guys from our local Land Rover club - they watch out for my "Henry" and spot me through more difficult obstacles.
Overall I think we have all been surprised at how well Henry has done w/the 20" and pirellis. The pirellis also make for a smooth on-road ride. Initially I was in a rush to replace the set with 18" compo rims & nittos - but decided in the scheme of things, I would rather spend the money on rock slides and other more important off road accessories.
Having said all of that - if you are considering buying a rig that has the set up already on it - it's not a bad thing. If you are ok w/damage to your rims - it will serve you quite adequately in the majority of trail runs. Normally the limiting factor for me on whether or not to do a trail is if I might incur body damage, not if my tires will hold up.
if you have the stock 19" and are looking to swap out the set out - then I would go with the 18" compo rims w/nittos (or similar) as both options will set you back at least $2500.
Hope that helps..
