The maximum offset would depend on the width of the wheel chosen, and the overall diameter of the tire used. Hence the different offsets you found.

You may be able to make some implications by charting the width and offset of a number of wheels and the tire sizes reccomended. You might even make scale drawings of the different combinations and compare them to the ones on your car now. After you do the drawings, you could turn your wheels full lock both ways and make clearance measurements then check out how the different sizes would affect clearances. Don't forget to account for suspension movement.

The results would make a nice post.

There are plenty of postings to be found if you do a search.

If you are fitting wider wheels, I doubt that a large difference in offset would work.
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2 8s & 2 7s 600,000 miles total