>>>>
>>>>I have tried the XLSXWorkbook class. It opens a small XLSX file quickly. But one with 20,000 rows takes a very long time but perhaps I do something wrong (although I only change the filename ...?) Anyway, I found another tool which seems very powerful - https://www.coolutils.com/TotalExcelConverter - very fast conversion.
>>>
>>>Just made an experiment with a 10MB/160k rows XLSX file. It is ingested by an XLSX reader class of mine that rely heavily on the XML parser to hold and process data (there is only a cursor for shared strings, that is, the strings that are used in the spreadsheet) in 14 seconds. The same file, imported by LibreOffice Calc, takes 12 seconds to load (of course, LO Calc has to transform the file into ODF format, in the process).
>>>
>>>Although these are not actual figures for XLSXWorkbook, I believe theirs should not be too far away. In perspective, such timings seem acceptable to me.
>>
>>I tried XLSXWorkbook - takes far, far longer than that. In fact, I just killed VFP - I could see this was not going to be a realistic solution for my needs. Total Excel Converter from CoolUtils converts in 2 seconds or less (20k rows x 7 cols).
>
>Just for closure: stripped down the XLSX I used for testing to 20k rows x 23 cols and it loads in 3 seconds (no other processing than loading).
>
>Anyway, the available XSLX libraries (Greg's and Vihlelm's, the ones that I know of) offer much more than conversion services so probably will deserve your revisit in case you'll need something more from the XLSX files you have to process.

Yes, absolutely. The XLSXWorkbook is awesome and I'm sure I can use it. Greg did a great job there, it is very cool! I will check my XLSX file again - perhaps there is something wrong with it but I did re-save it (twice) using Excel 2010 to a new filename and got the same result? Anyway, thanks for your feedback!