Marshall, indeed, your TableMatrix seems to do the trick, at least performance-wize. It is significantly faster than my old "widget by widget" solution. As most of my cells are simple text fields with just the occasional Combobox and Checkbox, a lot less widgets now need to be created.

However, autosizing of columns I do miss from before when using the grid() packer to keep track of my "spreadsheet". Maybe someone knows of a solution?
In my grid() packer solution, I simply set the width of my widgets to 0 and the geometry manager itself (or maybe the widgets themselves?) auto calculated the necessary width. Is there some means of doing this also for TableMatrix? I guess adding a method for it myself would be doable otherwize.

Again, thanks for all your help. Bummer I didn't find TableMatrix myself.