For all of the 18inch compo' advocates...they are not in my budget ...
A. the reason you're finding different offsets is because they are replica wheels which are going to be ruined off-road as they are not usually made as strong or finished as durably. Thus, cheap, is in the end, also 'cheap'. Often in the long run, cheap becomes expensive.
B. you'll want the largest offset number (which is tightest stance) because they will rub into the frame horns if you use that tire diameter of 31.8 and 9.6" tread width. I had a 285/50-20 on my first lr3 but it was on genuine range rover sport supercharged "stormer" wheels.
Same look, but stronger build and the ideal offset. Though I don't recall that ET spec, you could dig it up on the internet. The 285 was wider but the overall diameter was not as big so no rubbing on all the turning and flex points. The almost rub spot was against the upper control arm right behind the tire. This will actually be the tightest when the vehicle is raised or the suspension is dropping the most. You can test this on a lift or at home by lifting the front end so that both tire dangle.
C. perfect tire for general forest roads, easier Moab type stuff yet while not being too bad even up to 100 mph on the highway at times if your psi is correct and higher than the door says for smaller street tires. That size is not E load but it is at least a D with max load at 65 psi so you could run at 48 no problem on a stock vehicle or even 50-52 if you start loading it up with rack, roof tent, bull bar, or sliders, or stock but 5-7 people (humans are heavy LOL ) A higher psi, if loaded up, will help with better vehicle stability while cornering, evasive maneuvers, and even long sweeping curves at 80 mph like you find in Idaho, MT, OR, CO, canyons, etc where speeds are still high.
D. That width is perfect for a range of no less than 8.5 and up to 9.5 wheel but I swear the genuine stormer was 9". My experience has been that when a wider section tire is stuffed on to a wheel too narrow, it handles like ****, seriously. As an example, for 8" wheel widths, a 285/60x18 is not as good handling feeling as a 265/65x18 and a 275/70x18 is much better than a 285/65x18. This is the same on cars. My BMW came stock with 245/40-18. I tried a 255/40 and it truly sucked, horrible in sweeping curves but a 245/45 is great even up to 155 mph. When you can see the splay out from the wheel too much, it's a sign the tire is not the ideal width relative to wheel width.
It's actually a very simple geometry explanation. The wider tread results in a trapeziod with wider side to the ground whereas the narrower or equal width tread results in a more square inflated shape (ignoring the sidewalls bulging out of course, just the 4 points in section are what matter). You can then imagine that the most stable tire proportions are where there is the slightest upside down trapeziod to almost square. When inflated it cannot shift as easily under side load.
In the special case of the LR3/4/RRS platform with it's funky control arm arrangements, weird frame "horns" behind the front tires, and goofy rear wheel well bulging areas to rub against, a wide tire tread and section becomes a huge PITA to fit if you care to retain actual wheel articulation and 100% of it's turning capability in lowered or raised modes.
E. lastly, that tire size you mention is kind of perfect IF you do the few physical modifications. If not, it will likely rub at those spots due to it's tread and section width which is about an inch wider than the standard "fits for sure with no mods" size of 265/65x18. While the 18 is only .3" smaller diameter, 31.5 vs 31.8, the issues comes from it's much wider tread and also the resulting wider offset which is required for a 9 or 9.5.
For a no-mods needed fit using your listed choices, would be on the 20x8.5 and ET 58 though with it that snug to the UCA, it'll be close, but the other two being wider wheels PLUS wider offset, will rub for sure. They'd look cool as **** though LOL.
To wrap this up for you, consider this, your "budget" may say the replica wheel is the 'right' choice. How long will you keep this vehicle and will you ever want the killer plush ride on even forest roads with no worries to go into the most rugged places on an 18" with even taller but narrower tire?
Nobody wants to buy beat up 20's that are meant to be pretty and have no dented lips. Plenty of people would be willing to buy used Compomotive wheels though. The compos are also engineered for more rugged use. A city example is that with an 18 and BFG ko2, you can parallel park via the pull in and curb drop method where you roll onto the curb with the right front wheel, then drop in. That's a sure way to **** up some **** 20's though....
Theft, your **** 20's are a target while dirty 18's are not.
The compos are designed for the very least amount of offset needed. They were literally built for the vehicle.
Don't forget you need to have 5 matching wheels and tires in event of a flat as you cannot use a different size spare.
Mudtech has a sweet and less commonly seen 18" too. Shipping isn't cheap but the wheels are about $300 each so honestly not expensive. You did buy a late model LR4 after all, budget was not a huge factor.