Well, Aspose.Cells.GridWeb does not put any restrictions at all, it depends upon MS Excel file formats (e.g XLS, XLSX etc.). Aspose.Cells.GridWeb follows MS Excel standards.
e.g (you may have the following in a single worksheet)
XLS —> you may have 65536 rows and 256 columns.
XLSX --> you may have more than 1 million records with long list of columns.
For performance issue, please try our latest version Aspose.Cells.GridWeb v188.8.131.52xxx (you may get it after installing Aspose.Cells for .NET v8.0.1 package). Also see the topic that may help you a bit for your reference: