Thanks for your query.
We know performance is a critical factor when choosing any approach or methodology to build a solution. Aspose.Cells for .NET is scalable, flexible and fast. Generally, we take it into account that users applications (using Aspose.Cells) might be simultaneously used by 100s of users. The API is fully stable and can perform spreadsheet tasks flawlessly whether on a single server, powering a single application or on a load-balanced web farm powering an enterprise-wide application.
Regarding performance matrices for writing large data set in Excel spreadsheet, see the document for your reference. We do have concrete performance matrices and benchmarks, it might not cover reading/write larger files but it does covert reading, writing operations and comparison with other products in the market (We do not mention our competitors’ names for certain reasons too.). Well, in short, the reading and saving operations are quite fast, you may evaluate the feature(s) with larger files by yourself.
By the way, Aspose.Cells also provides light weight model named LightCells for the purpose (writing and reading large data in Excel spreadsheet), e.g The LightCells API is useful for creating huge Excel spreadsheets quickly and efficiency. See the document for your reference:
so, you may test it by yourself and judge on how how many million data rows are added in less time.
Should you have any further queries, let us know and we will be happy to assist you soon.