... it uses 1.0GB memory after parsing an xls-file with a single worksheet and 64772 rows and 120 columns.
Yes, the claim of "no memory overhead" is a bit of a mistake/exaggeration. But you would get the same result using just Spreadsheet::ParseExcel with the CellHandler and NotSetCell options (which S::PE correctly says "reduces" memory overhead, not has "no" memory overhead). Spreadsheet::ParseExcel parses and saves a bunch of stuff before it even gets to the cell data. So the S::PE with the CellHandler/NotSetCells options and/or S::PE::Stream only save you from storing the cell data in memory. I don't know if it would be possible to tell S::PE to not save the metadata before the cell data (or possible to modify it to implement such a thing). Only jmcnamara would know for sure..