What do you mean with 'for a cell'?

I tried storing a 50kilobyte string (~50000 chars) at position 1,1 of a table - no errors, I could save, load and change it.

[in addition]
I already tried saving a 16 mb table in a file, with around 10000 strings in it. This lasted quite long, means around 20 seconds (without threading the save function the engine stops for that time!!). You shouldn't save that many data in only one table, not because of save / load time but for access speed matters.
It is definately better to create a small amount of big strings and store it to quite little positions than create hundreds of thousand small strings.