this one is by no means close to the longest thread, check out the g4 disco for sale thread where the seller misrepresented his vehicle.
Your posts are very confusing or you are confused.... I have photos of when there were 20" Range Rover Sport 10Y spoke wheels. You asked about that however said you have 19" tires and now refer to "RR". A "RR" is not a RRS and not the same base platform whereas the LR3 and RRS are and I think have the exact same offset or so close to not be an issue.
The wheels I had were 20" x9" any 19" rims, RR or RRS, will not be 9" wide and therefor even less of any issues in offset. why would you bother buying some RR or RRS 19" rims just to utilize one of the crappiest tires ever put on a rover of any year or model? Not to mention, the 19" rims made for the LR3 look better on the lr3 than the other model 19's. The 20's I had looked cool on a stock lr3 but silly on one with any other stuff.
If yours is going to stay more or less stock other than a roof rack, you might really dig the look and feel of the 20's. The wider tread seemed to really improve the cornering, not that the lr3 is supposed to feel like a race car, but it did help and the width was more proportional to the body design as the 9" rims stand outboard just a tad more to look more squat and tough. You can either use the stock sized 275/45x20 or upsize just barely to 285/50 ish to get a much better wheel well fill visually as well as more sidewall in a 20" wheel. I had the larger ones on my 06 lr3 and the smaller ones on the one in the photos. Both will fit in the stock spare slot.