My suggestion would be is get the best grip on the etymology of the Iberg (and/or its variants) surname and study how the spelling of the phonetic meaning varied by region. All people automatically can't be seen as genealogically connected for sole reason of having the same surname, but then all people ARE connected without a doubt. Generally, for Germanic people don't get hung up over a "y" being interchanged for an "i" in the old days. In 1863 my ggr-grandfather's brother can be found as "Heydel" and their father as "Heidel" on the same passenger ship list!
As for Ibergs once in Madison County, Ill how well do you their genealogy? There has appeared in the censuses to be a connection Ibergs from Switzerland had with Heidels from Baden.